Minerals | By_Name | By_Class | By_Groupings | Search | Sulfides

THE MINERAL CINNABAR

Chemistry: HgS, Mercury Sulfide●

Class: Sulfides and Sulfosalts●

Uses: primary ore of mercury, a pigment and as a minerals specimen.●

Specimens●

Cinnabar is a colorful mineral that adds a unique color to the mineral color palette. Its cinnamon toscarlet red color can be very attractive. Well shaped crystals are uncommon and the twinned crystals areconsidered classics among collectors. The twinning in cinnabar is distinctive and forms a penetrationtwin that is ridged with six ridges surrounding the point of a pryamid. It could be thought of as twoscalahedral crystals grown together with one crystal going the opposite way of the other crystal. Cinnabarwas mined by the Roman Empire for its mercury content and it has been the main ore of mercurythroughout the centuries. Some mines used by the Romans are still being mined today. Cinnabar sharesthe same symmetry class with quartz but the two form different crystal habits.

PHYSICAL CHARACTERISTICS:

Color is a bright scarlet or cinnamon red to a brick red.●

Luster is adamantine to submetallic in darker specimens.●

Transparency crystals are translucent to transparent.●

Crystal System is trigonal; 32●

Crystal Habits: individual, well formed, large crystals are scarce; crusts and crystal complexes aremore common; may be massive, or in capilary needles. Crystals that are found tend to be the sixsided trigonal scalahedrons that appear to have opposing three sided pyramids. It also formsmodified rhombohedrons, prismatic and twinned crystals as discribed above.

●

Cleavage is perfect in three directions, forming prisms.●

Fracture is uneven to splintery.●

Hardness is 2 - 2.5.●

Specific Gravity is approximately 8.1+ (very heavy for a non-metallic mineral)●

Streak is red●

Associated Minerals are realgar, pyrite, dolomite, quartz, stibnite and mercury.●

Other Characteristics: silghtly sectile and crystals can be striated.●

Notable Occurances include Almaden, Spain; Idria, Serbia; Hunan Prov., China and California,Oregon, Texas, and Arkansas, USA.

●

CINNABAR (Mercury Sulfide)

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Best Field Indicators are crystal habit, density, cleavage, softness and color.●

Minerals | By_Name | By_Class | By_Groupings | Search | SulfidesCopyright © 1995,1996 by Amethyst Galleries, Inc.

CINNABAR (Mercury Sulfide)

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Minerals | By_Class | By_Groupings | Search

Minerals by NameA B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Choose a letter of the alphabet from the above list, and the minerals will be listed that begin with thatletter.

The mineral name itself is a link to the description of that mineral species, while the number to the left isthe approximate count of the number of specimens currently available for sale of that species, and is alsoa direct link to the list of specimens.

The count may be zero, but if the link is active then there are specimens available to view, just notcurrently for sale. If the count is zero and the link is not active, then there are not even any specimens inthe database. Remember, there may be more than one page of specimens, so you may need to selectNext Page one or more times to see the entire list of available specimens.

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Minerals By ClassMinerals can be organized, mainly according to

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MINERALS

By NameA list of minerals inalphabetical order

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Interesting GroupingsGemstones, Birthstones,

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Elements Class: The Metals and their alloys and the Nonmetals.●

Sulfides Class: The Sulfides, the Selenides, the Tellurides, theArsenides, the Antimonides, the Bismuthinides and the Sulfosalts.

●

Halides Class: The Fluorides, the Chlorides and the Iodides.●

Oxides Class: The Oxides and the Hydroxides.●

Carbonates Class: The Carbonates, the Nitrates and the Borates.●

Sulfates Class: The Sulfates, the Sulfites, the Chromates, theMolybdates, the Selenates, the Selenites, the Tellurates, the Telluritesand the Tungstates (or the Wolframates).

●

Phosphates Class: The Phosphates, the Arsenates, the Vanadates andthe Antimonates.

●

Silicates Class: The Silicates (the largest class).●

The Organics Class: The "Minerals" composed of organicchemicals!

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Significant Element: Includes ores of metals such as lead orCopper.

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Meteoritic Minerals: Minerals found in meteorites.●

Minerals that Twin: These minerals may form twinned crystals.●

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Minerals by Locality: Some notable mineral sites and theminerals found there.

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Mineral SearchA Glossary of Terms is available which describes the consistent set of terms used in this mineraldatabase, and offers suggestions for effective searching. Try to use several independent descriptivewords, since "very heavy" will also match "heavy" and "very soft". Also, don't use negatives (such as"not transparent").

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The Sulfides ClassAs well as the Selenides, the Tellurides, the Antimonides, the Arsenides

and the Sulfosalts.

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The members of the Sulfide Class form an economically important class ofminerals. Most major ores of important metals such as copper, lead andsilver are sulfides. Strong generalities exist in this class. The majority ofsulfides are metallic, opaque, generally sectile, soft to average in hardnessand they have high densities, black or dark colored streaks and an igneousorigin. But, there are a few vitreous and transparent members such asrealgar, cinnabar and orpiment that tend to break the mold, so to speak.

Minerals belonging to the selenide, telluride, antimonide and arsenidesubclasses have very similar properties to the more common sulfides and arethus included here. The whole or partial supplanting of sulfur by eitherselenium, tellurium, antimony, arsenic or bismuth is possible because theseelements have similar sizes, charges and ionic strengths. Only minerals inthe sulfide class that have no appreciable sulfur are included in thesesubclasses. If there is enough sulfur in the mineral to be named in theformula than it is treated as a normal sulfide.

Except in the case of the Sulfosalts. This is a large segment of the sulfideclass whose difference from the other sulfides lies in the position of thesemi-metal ions. In most ordinary sulfides that contain a semi-metal such asantimony, arsenic or bismuth, they substitute in the sulfur positions, but insulfosalts they substitute for the metal ions and bond with the sulfurs. Theterm sulfosalts came from a theory that these minerals were the salts of acidsin which the oxygens are replaced by sulfurs. Such as Na2SO4 is the salt ofH2SO4 or sulfuric acid; then enargite, Cu3AsS4. would be the salt of thehypothetical acid H6AsS4. This theory is not considered credible now butthe name "sulfosalt" still persists.

These are some of the members of the Sulfide Class:

The Standard Sulfides:

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Acanthite/Argentite (Silver Sulfide)●

Aguilarite (Silver Selenium Sulfide)●

Alabandite (Manganese Sulfide)●

Argentopentlandite (Silver Iron Nickel Sulfide)●

Argentopyrite (Silver Iron Sulfide)●

Argyrodite (Silver Germanium Sulfide)●

Arsenopyrite (Iron Arsenic Sulfide)●

Bismuthinite (Bismuth Sulfide)●

Bornite (Copper Iron Sulfide)●

Carrollite (Copper Cobalt Nickel Sulfide)●

Chalcocite (Copper Sulfide)●

Chalcopyrite (Copper Iron Sulfide)●

Cinnabar (Mercury Sulfide)●

Cobaltite (Cobalt Arsenic Sulfide)●

Covellite (Copper Sulfide)●

Cubanite (Copper Iron Sulfide)●

Digenite (Copper Sulfide)●

Famatinite (Copper Antimony Sulfide)●

Galena (Lead Sulfide)●

Germanite (Copper Germanium Gallium Iron Zinc Arsenic Sulfide)●

Gersdorffite (Nickel Arsenic Sulfide)●

Glaucodot (Copper Iron Arsenic Sulfide)●

Greenockite (Cadmium Sulfide)●

Hauchecornite (Nickel Bismuth Antimony Sulfide)●

Hauerite (Manganese Sulfide)●

Jalpaite (Silver Copper Sulfide)●

Kermesite (Antimony Oxysulfide)●

Laurite (Ruthenium Sulfide)●

Lautite (Copper Arsenic Sulfide)●

Linnaeite (Cobalt Sulfide)●

The Mineral Gallery - Sulfides Class

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Marcasite (Iron Sulfide)●

Metacinnabar (Mercury Sulfide)●

Millerite (Nickel Sulfide)●

Molybdenite (Molybdenum Sulfide)●

Orpiment (Arsenic Sulfide)●

Patronite (Vanadium Sulfide)●

Pentlandite (Iron Nickel Sulfide)●

Polydymite (Nickel Sulfide)●

Pyrite (Iron Sulfide)●

Pyrrhotite (Iron Sulfide)●

Realgar (Arsenic Sulfide)●

Rheniite (Rhenium Sulfide)●

Schollhornite (Hydrated Sodium Chromium Sulfide)●

Siegenite (Cobalt Nickel Sulfide)●

Sphalerite (Zinc Iron Sulfide)●

Stannite (Copper Iron Tin Sulfide)●

Sternbergite (Silver Iron Sulfide)●

Stibnite (Antimony Sulfide)●

Stromeyerite (Silver Copper Sulfide)●

Teallite (Lead Tin Sulfide)●

Tetradymite (Bismuth Tellurium Sulfide)●

Tungstenite (Tungsten Sulfide)●

Ullmannite (Nickel Antimony Sulfide)●

Wurtzite (Zinc Iron Sulfide)●

Subclass: SulfosaltsAikinite (Lead Copper Bismuth Sulfide)●

Andorite (Silver Lead Antimony Sulfide)●

The Mineral Gallery - Sulfides Class

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Baumhauerite (Lead Arsenic Sulfide)●

Berthierite (Iron Antimony Sulfide)●

Boulangerite (Lead Antimony Sulfide)●

Bournonite (Lead Copper Antimony Sulfide)●

Chalcostibite (Copper Antimony Sulfide)●

Cylindrite (Iron Lead Tin Antimony Sulfide)●

Dufrenoysite (Lead Arsenic Sulfide)●

Emplectite (Copper Bismuth Sulfide)●

Enargite (Copper Arsenic Sulfide)●

Franckeite (Lead Tin Iron Antimony Sulfide)●

Freieslebenite (Silver Lead Antimony Sulfide)●

Geocronite (Lead Antimony Arsenic Sulfide)●

Gratonite (Lead Arsenic Sulfide)●

Hutchinsonite (Thallium Lead Arsenic Sulfide)●

Jamesonite (Lead Iron Antimony Sulfide)●

Jordanite (Lead Thallium Arsenic Antimony Sulfide)●

Matildite (Silver Bismuth Sulfide)●

Meneghinite (Copper Lead Antimony Sulfide)●

Miargyrite (Silver Antimony Sulfide)●

Owyheeite (Silver Lead Antimony Sulfide)●

Polybasite (Silver Copper Antimony Sulfide)●

Proustite (Silver Arsenic Sulfide)●

Pyrargyrite (Silver Antimony Sulfide)●

Sartorite (Lead Arsenic Sulfide)●

Schapbachite (Silver Bismuth Sulfide)●

Semseyite (Lead Antimony Sulfide)●

Smithite (Silver Arsenic Sulfide)●

Stephanite (Silver Antimony Sulfide)●

Tennantite (Copper Arsenic Sulfide)●

Tetrahedrite (Copper Iron Antimony Sulfide)●

Wittichenite (Copper Bismuth Sulfide)●

Wittite (Lead Bismuth Selenide Sulfide)●

The Mineral Gallery - Sulfides Class

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Xanthoconite (Silver Arsenic Sulfide)●

Zinkenite (Lead Antimony Sulfide)●

Subclass: Selenides*

Berzelianite (Copper Selenide)●

Clausthalite (Lead Selenide)●

Eucairite (Silver Copper Selenide)●

Klockmannite (Copper Selenide)●

Tiemannite (Mercury Selenide)●

Umangite (Copper Selenide)●

Subclass: Tellurides*

Altaite (Lead Telluride)●

Calaverite (Gold Telluride)●

Coloradoite (Mercury Telluride)●

Empressite (Silver Telluride)●

Hessite (Silver Telluride)●

Kostovite (Copper Gold Telluride)●

Krennerite (Silver Gold Telluride)●

Melonite (Nickel Telluride)●

Nagyagite (Gold Lead Antimony Iron Telluride Sulfide)●

Petzite (Silver Gold Telluride)●

Rickardite (Copper Telluride)●

Sylvanite (Silver Gold Telluride)●

Subclass: Antimonides*

Aurostibite (Gold Antimonide)●

Breithauptite (Nickel Antimonide)●

Dyscrasite (Silver Antimonide)●

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Subclass: Arsenides*

Domeykite (Copper Arsenide)●

Lollingite (Iron Arsenide)●

Maucherite (Nickel Arsenide)●

Nickeline (Nickel Arsenide)●

Nickel-skutterudite (chloanthite) (Nickel Arsenide)●

Rammelsbergite (Nickel Arsenide)●

Safflorite (Cobalt Iron Arsenide)●

Skutterudite (Cobalt Arsenide)●

Smaltite (Cobalt Nickel Arsenide)●

Sperrylite (Platinum Arsenide)●

* These minerals are sometimes thought of as alloys of metals withsemi-metals and placed in the Elements Class.

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The Mineral Gallery - Sulfides Class

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Minerals | By_Name | By_Class | Sulfides | Cinnabar

Cinnabar SpecimensThis list can be limited to available items only.This is a partial listing. See the Next Page (earlier specimens)

# CIN-14, $125.00 Sold!Dims: 2.9 x 1.7 x 1.7" (7.4 x 4.3 x 4.3 cm) .... Wt: 5.8 oz.(163.9 g) .... Loc: Tongren, Guizhou Province, ChinaA single prismatic Cinnabar crystal rests on the graylimestone host rock of this small hand specimen. Thoughit is trigonal in form, it also is in the form of a penetrationtwin, so that it appears to have a six-rayed, pentagonal

cross-section. It has visible dimensions of 0.5 x 0.2 x 0.2" (1.3 x 0.5 x 0.5 cm) and is in pristinecondition, showing no human-induced damage whatsoever. Its form is also excellent, as all edges aresharp and all faces are striated but flat and clean, and possess a bright submetallic luster. Its redcoloration is so deep that it is nearly opaque to all intents and purposes, and its metallic luster providessome interference. The crystal rests on a bed of heavily intergrown rhombohedral dolomite crystals andis adjacent to a cluster of small, prismatic quartz crystals (see the close-up image).

# CIN-13, $140.00 Dims: 2.2 x 1.8 x 1.4" (5.6 x 4.6 x 3.6 cm) .... Wt: 4.4 oz.(123.9 g) .... Loc: Tongren, Guizhou Province, ChinaA single, well-formed Cinnabar crystal rests on thedolomite-and-limestone base of this specimen. The crystalhas dimensions of 0.6 x 0.3 x 0.3" (1.5 x 0.8 x 0.8 cm),

and is in very good condition, showing two small spots of minor damage, one at the base of itstermination, and one at its tip. Its trigonal prismatic form is excellent; it occurs in the form of apenetration twin, so that when viewed from above, the termination is in the shape of a six-rayed star (seethe close-up image). Though a few are disjointed, most of its surfaces are well-defined and its faces arestriated but generally clean, and possess a submetallic and almost adamantine luster. It has the classicdeep red coloration of Cinnabar and is translucent under bright light, showing patches of dimtransparence in some areas. It rests on a bed of white dolomite that has good rhombohedral form but isheavily damaged, which in turn coats parts of the brown limestone base rock.

# CIN-12, $110.00 Dims: 2.4 x 2.1 x 1.7" (6.1 x 5.3 x 4.3 cm) .... Wt: 3.8 oz.(107.4 g) .... Loc: Tongren, Guizhou Province, ChinaThis small hand specimen consists of a single trigonalprismatic Cinnabar crystal that rests on a dolomiticlimestone base. It has visible dimensions of 0.5 x 0.2" (1.3

x 0.5 cm) and is in excellent condition- the only noticeable damage appears to be partly healed, and thusoccurred prior to the mining of the specimen. Its edges are well-defined and its faces are clean,possessing an adamantine, submetallic luster. It has the standard deep red coloration of this mineral and

Cinnabar Specimens

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is dimly transparent in halogen light. The crystal extends out of a hollow in the host rock that is line withmany small, dull, cream-colored dolomite rhombohedrons and a few tiny quartz crystals. When lookingdown into the crevice, one can see another, incomplete Cinnabar crystal that is heavily intergrown withboth the first crystal and the dolomites.

# CIN-11, $90.00 Sold!Dims: 3.3" x 2.9" x 1.8" (9.4 x 7.3 x 4.6 cm) .... Wt: 6.83oz. (193.7 g) .... Loc: Guizhou Province, ChinaThree undamaged Cinnabar crystals rest on thedolomite-and-limestone host rock of this specimen. Thelargest of these is also the most exposed, and hasdimensions of 0.4 x 0.2 x 0.2" (1.0 x 0.5 x 0.5 cm); the

smallest of the crystals is deeply embedded in the dolomite base, and is barely visible. All show excellenttrigonal prismatic form; the largest and smallest crystals show flat, basal terminations, whereas the othercrystal has a warped form that makes it appear to be nearly octahedral! All have the deep red color that isstandard for Cinnabar, and their luster is subadamantine-to-submetallic. Though it is difficult todetermine, I am relatively certain that all are transparent and clear. The dolomite crust from which theCinnabars extend is made up of dull, cream-colored intergrown rhombohedrons with curved edges. They,in turn, rest on a dark gray-brown base of dolomitic limestone. A large piece of a broken quartz crystalalso rests on the dolomite crust, and appears to contain several incomplete Cinnabar crystals that were tr

This was a partial listing. See the Next Page (earlier items)This list can be limited to available items only.Would you like to be notified when additional specimens are available? Yes

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Minerals | By_Name | By_Class | Sulfides | CinnabarAll images and descriptions Copyright © 1997 by Amethyst Galleries, Inc.

Cinnabar Specimens

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CINNABAR(Penetration Twin)

The Twinned Minerals

MINERALS

By NameA list of minerals inalphabetical order

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Physical PropertiesKeys to identifying minerals

Witherite(trilling)

Staurolite(penetration twin)

Twinned minerals have their own following in the mineral collectinghobby. There are collectors that are only interested in twinned minerals.Twins can add a fascinating side to otherwise boring minerals or can addyet another dimension to an already complex mineral such as calcite.There are several minerals that form classic twins such as chalcocite,fluorite, sanidine, microcline, harmotome, staurolite, gypsum, cinnabar,spinel and rutile to name a few (more are listed below). Some twinshave been given colloquial names such as the "fairy cross", "iron cross"and "cog wheel" twins.

Twins form as a result of an error during crystallization. Instead of a"normal" single crystal, twins will often appear doubled where twocrystals appear to be growing out of or into each other, like Siamesetwins. Some twins however are not even identifiable outwardly andsome minerals in fact have been found to be just a twinned variety ofanother mineral. Accidental relationships are not considered twins, suchas when two distinct crystals grow more or less randomly side-by-sideor toward each other, etc. Also epitaxial overgrowths are also not twins.These occur when one mineral of similar structure, but differentchemistry, grows onto and "continues" the earlier mineral's crystal. Atwin's formation is never random and follows certain defined rulescalled twin laws. Many types of twin laws are given their own uniquenames and some are well known, such as the Spinel Law or the AlbiteLaw.

The twin laws are crystallographic in nature and are caused by flaws inthe crystal structure that occur during growth or during changes inphases such as from a high temperature phase to a low temperaturephase. One example of how twins form is explained by looking at howcrystals grow. Most crystals grow by adding layers of atoms, one layerat a time (in a simplistic model). If the first layer is called A and the nextlayer which is in a different position is called B and the next C followedby another A and so forth, then a structure will be built like so:ABCABCABCABC . . . Many minerals form with such a stackingsequence. But, if an error occurs during growth a twin can be formed. Ifthe next layer of atoms becomes misplaced and assumes the wrongposition, then the following sequence will form:

Mineral Gallery - THE TWINNED MINERALS

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Quartz(Japan Law Twin)

Muscovite(Star Twins)

Calcite(Butterfly Twin)

Herderite(Fishtail Twin)

ABCABCABCACBACBACBA

Can you see the flaw? The C layer next to the middle A layer is wrongbecause there should be a B layer next. The rest of the sequence is thenrepeated as if nothing happened and the crystal grows outward in bothdirections until finished growing. Directly through the middle A layer, amirror plane is produced and the right side of the crystal will be a mirrorimage of the left side just as a left hand is the mirror image of the righthand. The mirror is easier to see if the A is replaced by a vertical line |which represents a mirror plane as in:

ABCABCABC | CBACBACBA

Not all twins are formed this way, but it gives a good idea of how a twinis possible.

Twins are recognized by penetration angles or notches in the crystal,mirror planes that do not normally occur on a specific mineral andcrystallographic techniques not normally available to the averagecollector. Twinning often has a dramatic effect on the outwardsymmetry of the mineral either by raising or lowering the symmetry.Twinning can make an orthorhombic mineral appear hexagonal or makea trigonal mineral appear monoclinic.

There are two general types of twin styles; contact and penetration.Contact twins have a composition plane (the twin plane) that forms atthe boundary between the two twins. The composition plane is a mirrorplane where the two twins can look like reflected images of each other(like a Siamese twin). The angle between the twins is critical and insome cases diagnostic. If the angle is 180 degrees then the crystals growaway from each other in opposite directions. If the angle is less than 180degrees then the twin will have a noticeable bend. These twins formdove-tail, fish-tail and chevron shaped twins.

Many twins form penetration twins which look like two crystals thatgrew into and out of each other. These twins have portions of theirrespective twins protruding out of each other on different sides. At timesit may look as if half the crystal was twisted in the wrong direction orthat whoever made the crystal didn't know how it was supposed to fittogether. The effect is really interesting on well formed twins. Thesetwins can form crosses, 3-D star shapes and complex structures.

In some minerals, these two types can be repeated again and again; two,three or nearly an infinite number of times. There are two types of repeattwinning; cyclic and lamellar. Lamellar, which is also calledpolysynthetic twinning, forms from contact twins repeating continuouslyone twin after another, even on the microscopic level. Eventually acrystal composed of stacked twin layers is the result. The Feldspar

Mineral Gallery - THE TWINNED MINERALS

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Diamond(Penetration Twin)

Orthoclase(Penetration Twin)

OTHERPROPERTIES:

Color●

Luster●

Diaphaneity●

Crystal Systems●

Technical CrystalHabits

●

Descriptive CrystalHabits

●

Twinning●

Cleavage●

Fracture●

Hardness●

Specific Gravity●

Streak●

Fluorescence●

Phosphorescence●

Triboluminescence●

Thermoluminescence●

Index of Refraction●

Birefringence●

Double Refraction●

Dispersion●

Pleochroism●

Group minerals are the masters of this type of twinning which for thefeldspars is know as the Albite Law.

If a composition twin has an angle of 30, 45, 60 or 90 degrees and itrepeats 3, 4, 6 or so times . . . then it could form a complete circle orcyclic twin. Some classic twins form cyclic twins called "trillings";where the mineral is composed of three twin components. Other cyclictwins can have 4, 6 or even 8 components, but trillings are the mostcommon.

Twinning is actually rather common in the mineral kingdom, howeverperfectly formed twins are not. Minerals that commonly grow wellformed twins are known to nearly every mineral collector. Twincollecting can be a very enjoyable hobby and most collectors own one ormore. Even collectors of specific types of minerals must have theirrespective twins in order to have a "complete" collection. The twinningphenomena is well studied in the science of mineralogy. The study oftwins is also important in crystallography, metallurgy, chemistry andbiology.

Minerals that can form interesting twins along with their typicaltwinning style:

Among the Elements:

Diamond (Spinel Law and penetration twins)❍

Among the Sulfides:

Arsenopyrite (cross-shaped twins)❍

Bournonite ("Cog Wheel" twins)❍

Chalcocite (pseudohexagonal cyclic twins)❍

Chalcopyrite (penetration twins)❍

Cinnabar (pentration twins)❍

Dyscrasite (pentration twins)❍

Enargite (star shaped cyclic twins)❍

Galena (Spinel Law twins)❍

Loellingite (penetration twins)❍

Marcasite (polysynthetic twining and"Cockscomb" twins)

❍

Pyrite ("Iron Cross" twins)❍

Sphalerite (complex; involving penetration andcontact twinning)

❍

Mineral Gallery - THE TWINNED MINERALS

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Asterism●

Chatoyancy●

Parting●

Striations●

radioactivity●

Magnetism●

Odor●

Feel●

Taste●

Solubility●

Electrical properties●

Reaction to acids●

Thermal properties●

Associated Minerals●

Notable Localities●

Phantoms●

Inclusions●

Pseudomorphs●

Meteoritic Minerals●

Stibnite (bent angles on elongated crystals)❍

Tetrahedrite (penetration twins)❍

Wurtzite (fourling twins)❍

Among the Halides:

Boleite (pseudo-cubic twins)❍

Fluorite (classic penetration twins)❍

Among the Oxides:

Cassiterite (classic trillings)❍

Chrysoberyl (hexagonal trillings)❍

Rutile (classic eightlings and sixlings, "sagenite"lattice twinning and "elbow" twins)

❍

The Spinel Group minerals (Spinel Law twins)❍

Among the Carbonates:

Aragonite (pseudohexagonal trillings)❍

Calcite (four different contact twins)❍

Cerussite (pseudohexagonal trillings and chevrontwins; the very best reticulated twin structures)

❍

Leadhillite (pseudohexagonal trillings and ArtiniLaw twins)

❍

Witherite (pseudohexagonal pyramidal trillings)❍

Among the Sulfates:

Gypsum (fishtail and dove-tail twins)❍

Spangolite ("hatchet" twins)❍

Among the Phosphates:

Amblygonite (flattened elongated twins)❍

Herderite (fishtail twins)❍

Monazite (penetration twins)❍

Among the Silicates:

Chabazite (simple and complex penetration twins)❍

Epididymite (six sided tabular trillings and fish-tailtwins)

❍

Mineral Gallery - THE TWINNED MINERALS

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Eudidymite (tabular star shaped twins)❍

All of The Feldspar Group of Minerals especially:

Albite (Manebach, Carlsbad, Baveno and ofcourse Albite Law lamellar twins)

■

Andesine (Manebach, Carlsbad and AlbiteLaw lamellar twins)

■

Labradorite (Albite Law lamellar twins)■

Microcline (Manebach, Carlsbad and AlbiteLaw lamellar twins)

■

Oligoclase (Manebach, Carlsbad and AlbiteLaw lamellar twins)

■

Orthoclase (Manebach, Carlsbad and AlbiteLaw lamellar twins)

■

Sanidine (Manebach, Carlsbad and AlbiteLaw lamellar twins)

■

❍

Harmotome (Stempel, Perier and Marburg Lawtwins forming complex cross-like penetrationtwins)

❍

Muscovite ("star" twins)❍

Neptunite (penetration twins)❍

Phenakite (penetration twins)❍

Phillipsite (Harmotome-like twins)❍

Quartz (Japan Law, Dauphine Law, Brazil Law andothers)

❍

Sphene/Titanite (contact twins)❍

Staurolite (cross-shaped twins gave it its name)❍

Tridymite (six rayed trillings)❍

Minerals | By_Name | By_Class | By_Groupings | Search | Physical Properties

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Mineral Gallery - THE TWINNED MINERALS

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Minerals | By_Name | By_Class | By_Groupings | Search | Properties | Sulfides

THE MINERAL REALGAR

Chemistry: AsS, Arsenic Sulfide●

Class: Sulfides and Sulfosalts●

Uses: A major ore of arsenic, formerly used for pigments, firework coloring agent and asmineral specimens.

●

Specimens●

Realgar is an oddball among the sulfides. It is one of only a few sulfides that are not metallic or opaqueor blandly colored. Its structure is analogous to that of sulfur and resembles sulfur in most respectsexcept for color (the name "ruby sulfur" has been applied to realgar). Sulfur has a structure composed of8 sulfur atoms linked in a ring. Realgar's structure alternates between sulfur atoms and arsenic atomsproducing rings of As4S4. The arsenic atoms affect the structure altering it from sulfur's orthorhombicsymmetry to realgar's monoclinic symmetry.

Realgar occurs in hydrothermal veins with valuable metal sulfide ores and its bright red color can be anaid to prospectors. It also can be found in hot spring deposits and as a volcanic sublimate product(crystallizing from vapors). Realgar gets its name from the Arabic words for "powder of the mine" (rahjal ghar). Realgar is famous for some wonderfully beautiful specimens. Some specimens can have a deepruby red color with an amazing clarity and a high luster. The color of realgar is truly something toappreciate and cherish. But realgar's beauty is sometimes fleeting.

It is an unstable mineral and will alter to a different mineral, pararealgar and eventually to a powder.This process takes time and is accelerated by exposure to light. Specimens should be stored in dark,enclosed containers, and only exposed to light for the brief enjoyment of its owner and friends. Thissounds extreme, but wonderfully beautiful realgar specimens are worth preserving for as long aspossible. If you are wondering how quickly the deterioration occurs, the answer is immediately, butfortunately very slowly. Ancient Chinese carvings of realgar are still in existence, but badly affected bythe deterioration. The deterioration of realgar was thought to produce the closely related yelloworpiment, but this was recently proven to be false and the deterioration product is in fact yellow-orangepararealgar. In old paintings and manuscripts, realgar was a common pigment for paints and dyes. Manyof these paintings now have a yellow or orange hue where once the color must have been an original red.

PHYSICAL CHARACTERISTICS:

Color is orange to red.●

Luster is resinous, adamantine to sub-metallic.●

Transparency: Crystals are translucent to transparent.●

REALGAR (Arsenic Sulfide)

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Crystal System: Monoclinic; 2/m.●

Crystal Habits: include prismatic striated crystals with a rounded diamond-like cross-section.They are terminated by a wedge-like dome. Also found as grains, crusts and earthy masses.

●

Cleavage is good in one direction.●

Fracture is subconchoidal.●

Hardness is 1.5 - 2●

Specific Gravity is 3.5 - 3.6●

Streak is orange to orange-yellow.●

Other Characteristics: Realgar is unstable in light; specimens should be stored in completedarkness, rarely some specimens fluoresce under UV light and crystals are pleochroic betweendark red and orange red.

●

Associated Minerals almost always include orpiment, also calcite, stibnite and other metalsulfide ores.

●

Notable Occurrences include most importantly Hunan Province, China; but also Switzerland;Japan; Macedonia; Mercur, Utah, USA; Romania and many other localities.

●

Best Field Indicators are of course color as well as crystal habit, association with orpiment,softness and luster.

●

Minerals | By_Name | By_Class | By_Groupings | Search | Properties | SulfidesCopyright © 1995,1996,1999 by Amethyst Galleries, Inc.

REALGAR (Arsenic Sulfide)

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Minerals | By_Name | By_Class | By_Groupings | Search | Properties | Sulfides

THE MINERAL PYRITE

Chemistry: FeS2, Iron Sulfide●

Class: Sulfides●

Group: Pyrite●

Uses: A very minor ore of sulfur for sulfuric acid, used in jewelry under the trade name"marcasite" and as mineral specimens.

●

Specimens●

Pyrite is the classic "Fool's Gold". There are other shiny brassy yellow minerals, but pyrite is by far themost common and the most often mistaken for gold. Whether it is the golden look or something else,pyrite is a favorite among rock collectors. It can have a beautiful luster and interesting crystals. It is socommon in the earth's crust that it is found in almost every possible environment, hence it has a vastnumber of forms and varieties.

Bravoite is the name given to a nickel-rich iron sulfide. It is closely related to pyrite but contains up to20% nickel. Some mineral books treat it as a variety of pyrite.

Pyrite is a polymorph of marcasite, which means that it has the same chemistry, FeS2, as marcasite; buta different structure and therefore different symmetry and crystal shapes. Pyrite is difficult to distinguishfrom marcasite when a lack of clear indicators exists.

Pyrite's structure is analogous to galena's structure with a formula of PbS. Galena though has a highersymmetry. The difference between the two structures is that the single sulfur of galena is replaced by apair of sulfurs in pyrite. The sulfur pair are covalently bonded together in essentially an elemental bond.This pair disrupts the four fold symmetry that a single atom of sulfur would have preserved and thusgives pyrite a lower symmetry than galena.

Although pyrite is common and contains a high percentage of iron, it has never been used as a significantsource of iron. Iron oxides such as hematite and magnetite, are the primary iron ores. Pyrite is not asecomonical as these ores possibly due to their tendency to form larger concentrations of more easilymined material. Pyrite would be a potential source of iron if these ores should become scarce.

Pyrite has been mined for its sulfur content though. During WWII, sulfur was in demand as a strategicchemical and North American native sulfur mines were drying up. A sulfide deposit near DucktownTenn. was found to be able to mine pyrite and other sulfides such as pyrrhotite and pentlandite andproduce the needed sulfur as well as iron and other metals. The sulfur was used in the production ofsulfuric acid, an important chemical for industrial purposes. Now most sulfur production comes fromH2S gas recovered from natural gas wells.

PYRITE (Iron Sulfide)

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PHYSICAL CHARACTERISTICS:

Color is brassy yellow.●

Luster is metallic.●

Transparency: Crystals are opaque.●

Crystal System is isometric; bar 3 2/m●

Crystal Habits include the cube, octahedron and pyritohedron (a dodecahedron with pentagonalfaces) and crystals with combinations of these forms. Good interpenetration twins called ironcrosses are rare. Found commonly in nodules. A flattened nodular variety called "Pyrite Suns" or"Pyrite Dollars" is popular in rock shops. Also massive, reniform and replaces other minerals andfossils forming pseudomorphs or copies.

●

Cleavage is very indistinct.●

Fracture is conchoidal.●

Hardness is 6 - 6.5●

Specific Gravity is approximately 5.1+ (heavier than average for metallic minerals)●

Streak is greenish black.●

Other Characteristics: Brittle, striations on cubic faces caused by crossing of pyritohedron withcube. (note - striations on cube faces also demonstrate pyrite's lower symmetry). Pyrite unlike goldis not malleable.

●

Associated Minerals are quartz, calcite, gold, sphalerite, galena, fluorite and many otherminerals. Pyrite is so common it may be quicker to name the unassociated minerals.

●

Notable Occurrences include Illinois and Missouri, USA; Peru; Germany; Russia; Spain; andSouth Africa among many others.

●

Best Field Indicators are crystal habit, hardness, streak, luster and brittleness.●

Minerals | By_Name | By_Class | By_Groupings | Search | Properties | SulfidesCopyright © 1995,1996 by Amethyst Galleries, Inc.

PYRITE (Iron Sulfide)

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DOLOMITE

Chemistry: CaMg(CO3)2, Calcium Magnesium Carbonate●

Class: Carbonates●

Group: Dolomite●

Uses: in some cements, as a source of magnesium and as mineral specimens.●

Specimens●

Dolomite, which is named for the French mineralogist Deodat de Dolomieu, is a common sedimentaryrock-forming mineral that can be found in massive beds several hundred feet thick. They are found allover the world and are quite common in sedimentary rock sequences. These rocks are calledappropriately enough dolomite or dolomitic limestone. Disputes have arisen as to how these dolomitebeds formed and the debate has been called the "Dolomite Problem". Dolomite at present time, does notform on the surface of the earth; yet massive layers of dolomite can be found in ancient rocks. That isquite a problem for sedimentologists who see sandstones, shales and limestones formed today almostbefore their eyes. Why no dolomite? Well there are no good simple answers, but it appears that dolomiterock is one of the few sedimentary rocks that undergoes a significant mineralogical change after it isdeposited. They are originally deposited as calcite/aragonite rich limestones, but during a process calldiagenesis the calcite and/or aragonite is altered to dolomite. The process is not metamorphism, butsomething just short of that. Magnesium rich ground waters that have a significant amount of salinity areprobably crucial and warm, tropical near ocean environments are probably the best source of dolomiteformation.

Dolomite in addition to the sedimentary beds is also found in metamorphic marbles, hydrothermal veinsand replacement deposits. Except in its pink, curved crystal habit dolomite is hard to distinguish from itssecond cousin, calcite. But calcite is far more common and effervesces easily when acid is applied to it.But this is not the case with dolomite which only weakly bubbles with acid and only when the acid iswarm or the dolomite is powdered. Dolomite is also slightly harder, denser and never formsscalenohedrons (calcite's most typical habit).

Dolomite differs from calcite, CaCO3, in the addition of magnesium ions to make the formula,CaMg(CO3)2. The magnesium ions are not the same size as calcium and the two ions seem incompatiblein the same layer. In calcite the structure is composed of alternating layers of carbonate ions, CO3, andcalcium ions. In dolomite, the magnesiums occupy one layer by themselves followed by a carbonatelayer which is followed by an exclusively calcite layer and so forth. Why the alternating layers? It isprobably the significant size difference between calcium and magnesium and it is more stable to groupthe differing sized ions into same sized layers. Other carbonate minerals that have this alternating layeredstructure belong to the Dolomite Group. Dolomite is the principle member of the Dolomite Group of

DOLOMITE (Calcium Magnesium Carbonate)

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minerals which includes ankerite, the only other somewhat common member.

Dolomite forms rhombohedrons as its typical crystal habit. But for some reason, possibly twinning, somecrystals curve into saddle-shaped crystals. These crystals represent a unique crystal habit that is wellknown as classical dolomite. Not all crystals of dolomite are curved and some impressive specimensshow well formed, sharp rhombohedrons. The luster of dolomite is unique as well and is probably thebest illustration of a pearly luster. The pearl-like effect is best seen on the curved crystals as a sheen oflight can sweep across the curved surface. Dolomite can be several different colors, but colorless andwhite are very common. However it is dolomite's pink color that sets another unique characteristic fordolomite. Crystals of dolomite are well known for their typical beautiful pink color, pearly luster andunusual crystal habit and it is these clusters that make very attractive specimens.

PHYSICAL CHARACTERISTICS:

Color is often pink or pinkish and can be colorless, white, yellow, gray or even brown or blackwhen iron is present in the crystal.

●

Luster is pearly to vitreous to dull.●

Transparency crystals are transparent to translucent.●

Crystal System is trigonal; bar 3●

Crystal Habits include saddle shaped rhombohedral twins and simple rhombs some with slightlycurved faces, also prismatic, massive, granular and rock forming. Never found in scalenohedrons.

●

Cleavage is perfect in three directions forming rhombohedrons.●

Fracture is conchoidal.●

Hardness is 3.5-4●

Specific Gravity is 2.86 (average)●

Streak is white.●

Other Characteristics: Unlike calcite, effervesces weakly with warm acid or when first powderedwith cold HCl.

●

Associated Minerals: include calcite, sulfide ore minerals, fluorite, barite, quartz andoccasionally with gold.

●

Notable Occurrences include many localities throughout the world, but well known from sites inMidwestern quarries of the USA; Ontario, Canada; Switzerland; Pamplona, Spain and in Mexico.

●

Best Field Indicators are typical pink color, crystal habit, hardness, slow reaction to acid, densityand luster.

●

Minerals | By_Name | By_Class | By_Groupings | Search | Properties | CarbonatesCopyright © 1998 by Amethyst Galleries, Inc.

DOLOMITE (Calcium Magnesium Carbonate)

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Minerals | By_Name | By_Class | By_Groupings | Search | Properties | Silicates

THE MINERAL QUARTZ

Chemistry: SiO2 , Silicon dioxide●

Class: Silicates●

Subclass: Tectosilicates●

Group: Quartz●

Uses: silica for glass, electrical components, optical lenses, abrasives, gemstones, ornamentalstone, building stone, etc.

●

The Physical Properties of Quartz.●

Specimens

Additional variety specimens include:Amethyst❍

Citrine❍

Rock Crystal❍

Rose Quartz❍

Smoky Quartz❍

●

Quartz is the most common mineral on the face of the Earth. It is found in nearly every geologicalenvironment and is at least a component of almost every rock type. It frequently is the primary mineral,>98%. It is also the most varied in terms of varieties, colors and forms. This variety comes about becauseof the abundance and widespread distribution of quartz. A collector could easily have hundreds of quartzspecimens and not have two that are the same due to the many broad catagories. The specimens could beseparated by answers to the following questions: color?, shade?, pyramidal?, prismatic?, druzy?,twinned?, sceptered?, tapered?, phantomed?, inclusions?, coated?, microcrystalline?, stalactitic?,concretionary?, geoidal?, tappered?, banded?, etc. Multiple combinations of these could producehundreds of unique possibilities.

Some macrocrystalline (large crystal) varieties are well known and popular as ornamental stone and asgemstones.

Amethyst is the purple gemstone variety.●

Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heatingAmethyst.

●

Milky Quartz is the cloudy white variety.●

QUARTZ (Silicon Dioxide)

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Rock crystal is the clear variety that is also used as a gemstone.●

Rose quartz is a pink to reddish pink variety.●

Smoky quartz is the brown to gray variety.●

Cryptocrystalline (crystals too small to be seen even by a microscope) varieties are also used assemi-precious stones and for ornamental purposes. These varieties are divided more by character than bycolor. Chalcedony or agate is divided into innumeral types that have been named for locally commonvarieties. Some of the more beautiful types have retained their names on a world-wide basis while othernames have faded into obscurity. Some of the more common of these types are chrysoprase (a pure greenagate), sard (a yellow to brown agate), sardonyx (banded sard), onyx (black and white agate), carnelian(a yellow to orange agate), flint (a colorful and microscopically fibrous form), jasper (a colorful impureagate) and bloodstone (a green with red speckled agate).

Quartz is not the only mineral composed of SiO2. There are no less than eight other known structures thatare composed of SiO2. These other substances and quartz are polymorphs of silicon dioxide and belongto an informal group called the Quartz Group or Silica Group. All members of this group, exceptquartz, are uncommon to extemely rare on the surface of the earth and are stable only under hightemperatures and high pressures or both. These minerals have their own unique structures although theyshare the same chemistry, hence the term polymorph, which means many forms.

Quartz has a unique structure. Actually, there is another mineral that shares quartz's structure, and it isnot even a silicate. It is a rare phosphate named berlinite, AlPO4, that is isostructural with quartz. Thestructure of quartz involves corkscrewing (helix) chains of silicon tetrahedrons. The corkscrew takes fourtetrahedrons in order to repeat itself, or three turns. Each tetrahedron is essentially rotated 120 degrees.The chains are aligned along the c axis of the crystal and interconnected to two other chains at eachtetrahedron making quartz a true tectosilicate. This structure is not like the structure of the chain silicatesor inosilicates whose silicate tetrahedronal chains are not directly connected to each other. The structureof quartz helps explain many of its physical attributes.

For one, the helix makes three turns and this helps produce the trigonal symmetry of quartz. Likewise ahelix or corkscrew lacks mirror planes of symmetry as does quartz. The corkscrew structure would alsodisrupt any cleavage which requires a plane of weakness not found in quartz and breakage would resultin the curved fracture, conchoidal, that is found in quartz. Quartz can also have left and right handedcrystals just as a corkscrew can screw in a left handed way or in a right handed way. There are even somevery difficult to identify crystals of quartz that are twinned with alternating one sixths of the crystal beingright handed and then left handed.

Quartz is a fun mineral to collect. Its abundance on the Earth's surface is incredible and produces somewonderful varieties that don't even look like the same mineral. A collector must always be up on themany varieties of quartz and it sometimes embarrasses a collector to have collected too many specimensof such a common mineral. But nearly all collectors concede that you can never really have enoughquartz specimens.

QUARTZ (Silicon Dioxide)

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PHYSICAL CHARACTERISTICS:

Color is as variable as the spectrum, but clear quartz is by far the most common color followed bywhite or cloudy (milky quartz). Purple (Amethyst), pink (Rose Quartz), gray or brown to black(Smoky Quartz) are also common. Cryptocrystalline varieties can be multicolored.

●

Luster is glassy to vitreous as crystals, while cryptocrystalline forms are usually waxy to dull butcan be vitreous.

●

Transparency crystals are transparent to translucent, cryptocrystalline forms can be transparent,translucent or opaque.

●

Crystal System is trigonal; 32●

Crystal Habits are again widely variable but the most common habit is hexagonal prismsterminated with a six sided pyramid (actually two rhombohedrons). Three of the six sides of thepyramid may dominate causing the pyramid to be or look three sided. Left and right handedcrystals are possible and identifiable only if minor trigonal pyramidal faces are present. Druseforms (crystal lined rock with just the pyramids showing) are also common. Massive forms can bejust about any type but common forms include botryoidal, globular, stalactitic, crusts of agate suchas lining the interior of a geode and many many more.

●

Cleavage is not present.●

Fracture is conchoidal.●

Hardness is 7, less in cryptocrystalline forms.●

Specific Gravity is 2.65 or less if cryptocrystalline. (average)●

Streak is white.●

Other Characteristics: striations on prism faces run perpendicular to C axis, piezoelectric (seetourmaline) and index of refraction is 1.55.

●

Associated Minerals are numerous and varied but here are some of the more classic associationsof quartz (although any list of associated minerals of quartz is only a partial list): amazonite avariety of microcline, tourmalines especially elbaite, wolframite, pyrite, rutile, zeolites,fluorite, calcite, gold, muscovite, topaz, beryl, hematite and spodumene.

●

Best Field Indicators are first the fact that it is very common (always assume transparent clearcrystals may be quartz), crystal habit, hardness, striations, lack of cleavage and good conchoidalfracture.

●

Notable Occurances of amethyst are Brazil, Uraguay, Mexico, Russia, Thunder Bay area ofCanada, and some locallities in the USA. For Smoky Quartz; Brazil, Colorado, Scotland, SwissAlps among many others. Rose Quartz is also wide spread but large quantities come from brazil asdo the only large find of Rose Quartz prisms. Natural citrine is found with many amethyst depositsbut in very rare quantities. Fine examples of Rock crystal come from Brazil (again), Arkansas,many locallities in Africa, etc. Fine Agates are found in, of course, Brazil, Lake Superior region,Montana, Mexico and Germany.

●

Minerals | By_Name | By_Class | By_Groupings | Search | Properties | SilicatesCopyright © 1995 by Amethyst Galleries, Inc.

QUARTZ (Silicon Dioxide)

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THE MINERAL STIBNITE

Chemistry: Sb2S3, Antimony Sulfide●

Class: Sulfides●

Uses: An ore of antimony and as mineral specimens.●

Specimens●

Stibnite is a classic mineral species with fine crystal clusters and long curved crystals being the pride ofmany collectors. The slender curved metallic blades of stibnite can resemble arabian swords. The curvingof the long bladed crystals is due to twinning where one twin plane bends the crystal one direction andanother twin plane bends it in the other direction. This can occur numerous times down the length of onecrystal. Stibnite's crystal clusters are admired for their distinctive look with dozens of accicular or bladedcrystals jutting out in many divergent directions.

PHYSICAL CHARACTERISTICS:

Color is steel gray to silver.●

Luster is metallic.●

Transparency crystals are opaque.●

Crystal System is orthorhombic; 2/m 2/m 2/m●

Crystal Habits include bladed or acicular crystals often bent or curved due to twinning, alsogranular and massive.

●

Cleavage is perfect in the lengthwise direction.●

Fracture is irregular.●

Hardness is 2●

Specific Gravity is approximately 4.6+ (average for metallic minerals)●

Streak is a dark gray.●

Other Characteristics: striated lengthwise sometimes deeply, luster brighter on cleavage surfacesand crystals slightly flexible.

●

Associated Minerals include quartz, calcite, gold, arsenopyrite and other sulfides.●

Notable Occurrences include Hunan province, China; Japan; Germany; Brazil; Peru and SouthAfrica.

●

Best Field Indicators are crystal habit, softness and flexibility.●

STIBNITE (Antimony Sulfide)

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STIBNITE (Antimony Sulfide)

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Minerals | By_Name | By_Class | By_Groupings | Search | Elements

NATIVE MERCURY

Chemistry: Hg, Elemental Mercury●

Class: Elements●

Group: Gold●

Uses: Minor ore of mercury, electrical switches, thermometers●

Specimens●

Mercury is unique, as it is the only metal that is liquid at room temperature, having a melting point of -40C, and a boiling point of 357 C. This silvery liquid metal is very dense, yet has a high surface tension thatcauses is to form tiny little perfect spheres in the pores of the rocks it is found in. Many mineralogicalcharacteristics simply do not apply to a liquid: there is no "hardness", since it cannot be scratched (norcan it scratch); there is no crystal structure, no fracture, no cleavage, no streak; all of course, at roomtemperatures. When frozen, mercury forms crystals in the rhombohedral system at low pressure, and inthe tetragonal system at high pressure.

PHYSICAL CHARACTERISTICS:

Color is bright silvery metalic.●

Luster is metallic.●

Transparency is opaque.●

Crystal System does not apply●

Crystal Habits spherical droplets, or pools of mercury liquid.●

Cleavage does not apply●

Fracture does not apply●

Streak does not apply●

Hardness does not apply●

Specific Gravity is 13.5+ (very dense)●

Associated Minerals are cinnabar, calomel, and other secondary mercury minerals.●

Other Characteristics: Mercury is a liquid! It also expans at a constant rate with a rise intemperature.

●

Notable Occurrences include Almaden, Spain; Idrija, former Yugoslavia; Italy; California,Oregon, Texas, and Arkansas, USA.

●

Best Field Indicators its a liquid!●

MERCURY (Hg)

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MERCURY (Hg)

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