Native element Silver Ag (NOT REQUIRED FOR 3rd TEST) Diagnostic features: silvery, metallic luster on fresh surfaces (silver tarnishes quickly to brown or gray-black). High

specific gravity (G = 10.5). Cleavage: none. Hardness: 2.5 - 3. Malleable, ductile. Habit: crystals are usually malformed, as irregular masses, plates and scales. Sometimes found as wires or

arborescent (dendritic) groups. Look-alikes: other silver-coloured sulfides or sulfosalts (arsenopyrite, skutterudite) are brittle and have a lower

specific gravity.

Native element Copper Cu Diagnostic features: distinctive metallic luster and reddish-orange colour on fresh surfaces. Tarnishes to dark brown

colour. Cleavage: none. Malleable, with a hackly fracture. Hardness: 2.5 - 3 Habit: crystals are usually malformed, often in branching and arborescent groups. Look-alikes: nickeline (close in colour but harder).

Sulfide Covellite CuS (NOT REQUIRED FOR 3rd TEST) Diagnostic features: metallic luster, dark blue colour with a micaceous habit. Hardness: 1½-2. Cleavage: perfect {0001} basal cleavage on hexagonal tabular crystals. Habit: platy hexagonal crystals, or massive aggregates. Associations: covellite is usually found with other sulfide copper minerals (e.g., chalcocite, bornite and enargite) and

is derived from them by alteration. Look-alikes: none.

Native element Graphite C

Diagnostic features: dark gray, metallic to dull luster, greasy feel, soft enough to soil the fingers, unusually low

specific gravity (G = 2.23). Habit: rarely well crystallized, hexagonal plates and, less commonly, spherulites. Colour: dark gray (slightly brown in comparison to molybdenite). Streak: dark gray to black. Hardness (1-2, easily soils the fingers). Cleavage: perfect {0001} basal cleavage is rarely visible because the crystals are small or easily deformed. Look-alikes: Molybdenite. Graphite's gray colour is closer to beige while molybdenite’s gray has a bluish tinge. Also, be sure to compare their streak. Molybdenite has a greenish black streak.

Sulfide Stibnite Sb2S3 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: slender bladed crystals, perfect cleavage parallel to length, soft, black streak. Hardness: 2. Colour and streak: lead-gray to black. Metallic luster. Cleavage: {010} is parallel to elongation of the prism. Habit: prismatic habit, often striated vertically and often steeply terminated. Crystals are sometimes curved or bent.

Often in radiating groups or bladed forms with prominent cleavage. Look-alike: Galena (when massive). Massive stibnite is a darker grey than galena.

Sulfide Molybdenite MoS2 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: metallic luster, lead-gray colour with a bluish tone, soft and almost malleable (can be flaked

with the fingernail). Hardness: 1-1.5 Cleavage: {0001} perfect basal cleavage on tabular hexagonal crystals. Habit: hexagonal plates or short prisms. Often massive, commonly foliated. Look-alike: its greenish gray streak, and the bluish tone of its lead-gray colour distinguishes molybdenite from graphite's dark gray streak. Compare them carefully.

Sulfide Sphalerite ZnS Diagnostic features: moderate hardness (H = 3.5-4), many planes of cleavage, resinous luster. Habit: well-formed tetrahedral crystals (left, below) are rare. They cleave into dodecahedra (6 cleavage planes,

below right). Even in aggregates, the many cleavage planes give a “sparkling” appearance to the specimen. Colour: colourless when pure but generally yellow to brownish, sometimes black. The streak is colourless in pure

sphalerite and its colour is yellow to brown with increasing Fe content. Look-alikes: none, really. Hematite can be as sparkly but its streak is darker and slightly reddish. Sphalerite is the most common zinc mineral and it forms in hydrothermal vein systems, often with galena and other sulphides. The structure of sphalerite is a derivative of diamond's but its overall symmetry is lower because two different ions are in tetrahedral coordination.

Sulfide Chalcopyrite CuFeS2 Diagnostic features: deep brass-yellow colour, often tarnished in places to other colours (orange, purple, bluish). Habit: crystals are rare but when well-formed they are tetrahedra. Striations, if present, form triangles on faces. Colour: deep brass-yellow colour, with a greenish black streak. Hardness: 3.5-4 (easily scratched by knife but not by fingernail). Look-alikes: distinguished from pyrite by its deeper yellow colour, iridescent tarnish and lower hardness. Its tarnish

resembles bornite's but their colour on broken fresh surfaces is different. Distinguished from gold by its brittle nature, deeper yellow, and much lower density.

This copper sulfide is common, but is generally not a rich enough ore to be mined. However, hot waters from geothermal systems leach away copper from chalcopyrite, and re-deposit it as cuprite (Cu2O) or native copper.

Sulfide Pyrrhotite Fe1-xS Habit: pyrrhotite rarely forms good crystals, and is more commonly seen in massive aggregates. Under the

microscope, however, it may occur as (or contain) exsolution blebs and lamellae consisting of pentlandite (Fe,Ni)9S8, an important ore of Ni.

Colour: brownish bronze, metallic luster, black streak. Hardness: 4 Look alikes: pyrrhotite is close in colour and tarnish to chalcopyrite, but compare their streaks (pyrite and chalcopyrite have greenish black streaks). Pyrrhotite is also the only common ore mineral, with magnetite, to display magnetism. Its magnetism, though not as strong as that of magnetite, often helps to distinguish pyrrhotite from other yellow sulfides.

Sulfide Galena PbS Diagnostic features: high specific gravity, gray colour, metallic luster and cubic cleavage. Habit: usually cubic (left, below), but may be modified by octahedra (right, below). The cubic cleavage (center,

below) is often visible as broken sharp corners in coarse-grained aggregates. Colour: the lead gray colour of the mineral matches the colour of its streak. Hardness: 2.5 (very easy to streak) Look-alikes: stibnite when massive, but the cubic cleavage of galena is usually diagnostic. Galena is the more common of these two sulfides.

Sulfide Bornite Cu5FeS4 Diagnostic features: iridescent tarnish with blue, green and purple hues, but a bronze colour on fresh surface, and a grayish-black streak. Habit: its crystals (cubic or octahedral) are quite rare. Usually massive. No cleavage. Colour: the brownish bronze colour on fresh surfaces quickly tarnishes to purple. The mineral is sometimes called

"peacock ore" for its iridescent tarnish. Hardness: 3. Look-alikes: Chalcopyrite has a tarnish that may approach bornite but its fresh colour is a deeper yellow. Often found with other Fe and Cu sulfides (chalcocite, covellite, pyrite, chalcopyrite)

Sulfide Chalcocite Cu2S Diagnostic features: lead-gray colour on fresh surface, sectility and poor cleavage. Habit: well-formed crystals are uncommon. Cleavage is poor. Colour: lead-gray colour with metallic luster on fresh surface is brighter than its black, dull tarnish. Streak is grayish

black. Hardness: 2.5-3 Look-alikes: Enargite and stibnite are also dark grey but they do not tend to tarnish to a dull black. Enargite and

stibnite also have a better cleavage and prismatic habit. This very important copper ore is usually found with other Cu sulfides (covellite, chalcopyrite, bornite). It usually occurs as a secondary alteration of chalcopyrite or other primary copper minerals.

Sulfosalt Note: in a sulfosalt ( unlike in a sulfide, arsenide or sulfarsenide), some As acts as a cation. In this mineral, Ag and Sb are both cations, and sulfur is the sole anion. Pyrargyrite Ag3SbS3 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: dark reddish colour, occurrence with native silver (sometimes with Ag-bearing galena). Habit: well-formed crystals are rare. Colour: dark red. Hardness: 2-2.5

Sulfosalt Note: in a sulfosalt, unlike a sulfide, arsenide or sulfarsenide, some As acts as a cation. In this mineral, Cu and As both act as cations, and sulfur is the sole anion. Enargite Cu3AsS4 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: perfect prismatic cleavage, metallic luster and a matching grayish black colour and streak. Habit: crystals are generally tabular, columnar or bladed but the mineral also occurs as massive aggregates. Colour: grayish black, with a matching streak. Its metallic luster does not tarnish to a dull black as in chalcocite. Hardness: 3. Look-alikes: stibnite, chalcocite when massive. A rarer copper mineral, associated with covellite, pyrite, chalcocite, bornite and galena.

Sulfarsenide Note: in a sulfarsenide, both As and S play the role of anions. Arsenopyrite FeAsS (NOT REQUIRED FOR 3rd TEST) Diagnostic features: Metallic silver-white colour that may tarnish. Rhombic crystals striated along their short diagonal. Habit: twinning of orthorhombic crystals often produces striated aggregates. Distinct cleavage. Colour: silver-white. Streak: black. Hardness: 5.5-6. Look-alikes: Silver is more malleable, pyrite is isometric (usually cubic, octahedral or dodecahedral) and more

yellow. Look for the rhombic shape with striations. This is the most common ore of arsenic.

Arsenide Note: in an arsenide (as in a sulfarsenid), As plays the role of anion. Skutterudite (Co, Ni)As3 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: silver gray colour, metallic luster, black streak. Habit: isometric crystals are rarely distinct. Often forms cauliflower-like patches. No cleavage. Colour: silver gray. Streak: black. Hardness: 5.5-6. Look-alikes: arsenopyrite and silver are also silver or silvery gray but they tarnish to a dull dark gray. Skutterudite oxidizes to green or pink. This ore of cobalt or nickel is often identified in the field by the presence of oxidized crusts, called "copper bloom" when pink (the arsenate erythrite), or "nickel bloom" when green (the arsenate annabergite).

Sulfide Pyrite FeS2 Diagnostic features: pale brass yellow colour, relatively high hardness, streak is greenish to brownish black. Habit: crystals are often cubic, and usually striated (one direction on each face). Pyrite can also adopt other regular

forms like octahedra and dodecahedra, and some crystals combine two or three forms. Poor cleavage. Colour: pale brass yellow (deeper if tarnished) and metallic luster. Hardness: 6 (unusually high for a sulfide mineral). Look-alikes: massive chalcopyrite and other yellow sulfides are easily confused with massive pyrite until your eye

becomes attuned to their distinctly different colours and hardness. This is the most common sulfide, found in sedimentary, metamorphic and igneous rocks as well as hydrothermal deposits. It is often found with other sulfides.

Sulfide Marcasite FeS2 (NOT COMPULSORY FOR 3rd TEST) Diagnostic features: paler yellow to almost white colour on fresh fracture. Cockscomb or fibrous habit. Habit: crystals are orthorhombic and twinning can produce spear-shaped or cockscomb terminations (center, below).

"Pyrite suns" (right corner, below) are concretions of radiating fibrous crystals, usually formed as marcasite in sedimentary rocks, and generally later converted to its polymorph pyrite.

Colour: pale brass yellow to nearly white, tarnishes to metallic yellow or brown. Streak: grayish black. Hardness: 6-6.5 Look-alikes: Pyrite is a deeper yellow on its fresh surface and its crystals are isometric. Marcasite is a polymorph stable at somewhat lower temperatures (< 150 ºC) than pyrite. The two minerals commonly occur as pseudomorphs of one another.

Native element Sulfur S Diagnostic features: yellow colour, characteristic smell. Habit: usually found as incrustations or irregular masses that are imperfectly crystallized. When well formed the

crystals are orthorhombic and dipyramidal. Colour: yellow (but colour can tend towards orange or greenish when impurities substitute for S). Hardness: 1.5-2.5 Look-alikes: none. Note : Most of the specimens in your drawers are not examples of natural sulfur. They are chunks of the massive microcrystalline sulfur that is extracted from most oil or natural gas before they are sold as fossil fuels. If left in oil or gas, this sulfur would react with oxygen to form a serious atmospheric pollutant.

Carbonate (orthorhombic, aragonite structure) Cerussite PbCO3

Diagnostic features: high specific gravity (G = 6.55) and crystal form (often dendritic or in aggregates of criss-

crossing crystals). Association with Pb- and Zn-bearing sulfides and carbonates. Habit: single crystals are generally acicular, often dendritic. Colour: white. Streak: white (colourless). Look-alikes: Barite is close in specific gravity but more commonly tabular. Cerussite is often formed by the action of carbonated hydrothermal waters on galena. The alteration of galena (PbS) and sphalerite (ZnS), commonly found together and with pyrite (FeS2), gives rise to associations of secondary minerals which may include cerussite, smithsonite and limonite (a microcrystalline or hydrated form of goethite).

Carbonate (orthorhombic) Aragonite CaCO3

Diagnostic features: moderate hardness (H = 3.5-4), stronger effervescence in room-temperature HCl than other

common carbonate minerals (including calcite) and the lack of rhombohedral cleavage. Habit: single crystals are orthorhombic, often acicular or in radiating aggregates. The polysynthetic twins formed by

three intergrown crystals have a pseudo-hexagonal appearance (right, below), but their re-entrant angles are visible at the contact between the individual crystals.

Colour: generally colorless or white, but can be variously coloured by impurities. Look-alikes: Calcite has a lower hardness than aragonite and a distinctive rhombohedral cleavage. However, in many

deposits and in stalactites, where individual crystals are too small to be seen with the naked eye, X-ray diffraction is the best way to distinguish aragonite from calcite.

Calcite and aragonite are polymorphs of calcium carbonate. Calcite, less dense, is the more stable form at the Earth’s surface temperature and pressure. Some marine invertebrate (oysters, corals) secrete aragonite which, after the death of the animal, are replaced by the less soluble calcite during fossilization.

Arsenide Nickeline NiAs Diagnostic features: its pale copper red colour is distinctive. Habit: well formed crystals are rare. Colour: a distinctive pale copper red, tarnishing to dark gray or black. Streak is brownish black. Hardness: 5. Look-alike: Copper has a deeper colour. Nickeline often oxidizes to a pale green "nickel bloom" (the arsenate annabergite).

Sulfide Cinnabar HgS Diagnostic features: its red colour is somewhat variable but its scarlet streak is characteristic. Habit: well formed crystals are rare. Occurs as vein fillings or scattered among other sulfides. Colour: red (bright vermilion to brownish red) Hardness: 2.5 (very easy to streak, even when present as small grains) Look-alikes: none. This mineral is the only important ore of mercury.

Halide Halite NaCl Diagnostic features: low hardness (H = 2.5, scratched by a tough fingernail), perfect cubic cleavage, salty taste. Habit: crystals are usually cubic. “Hopper-shaped” skeletal crystals grow from rapidly evaporating solutions. Colour: colourless when pure. Often white because of inclusions (small bubbles filled with fluid that were trapped

during crystal growth) or coloured by impurities or inclusions of other minerals. Look-alikes: Sylvite tastes more bitter. The structure of halite, NaCl, and sylvite, KCl, are identical. Both minerals are less dense (G = 2-2.1) than most non-metallic minerals. They are part of a sequence of minerals commonly formed by evaporation of seawater: aragonite or calcite → gypsum → halite → sylvite.

Halide Sylvite KCl (NOT REQUIRED FOR 3rd TEST) Diagnostic features: low hardness (H = 2), perfect cubic cleavage, bitter taste (really awful). Habit: crystals are usually cubic, often modified by octahedral faces. Colour: colourless when pure, but natural crystals are often coloured by microscopic inclusions of other minerals or

the reddish remains of halophilic (i.e. salt-tolerant) algae which thrive in the evaporating saline water bodies where this mineral precipitates.

Specific gravity: G = 1.99, lower than that of most minerals with non-metallic luster. Look-alikes: Halite as a salty taste, less bitter than sylvite's. Identical in structure to halite (NaCl), but scarcer, sylvite forms at a later stage of seawater evaporation.

Halide Fluorite CaF2

Diagnostic features: octahedral cleavage, moderate hardness (H = 4, easily scratched by the knife), cubic habit. Habit: usually cubes, sometimes modified by octahedra. Often found in aggregates of interpenetrating crystals. Colour: very variable, the mineral is coloured by a wide range of impurities substituting for the Ca2+ ions. Cleavage: perfect, octahedral {111}. Look-alikes: None when its habit and cleavage are distinct. Most well crystallized fluorite is of hydrothermal origin but it also occurs widely as a disseminated phase in metamorphic and igneous rocks. The phenomenon of fluorescence received its name because it was observed early in some varieties of fluorite. Not all fluorite, however, is fluorescent. The property depends on the presence of trace amounts of rare-earth elements substituting for the Ca2+ ions in its structure. Avoid pouring dilute HCl on fluorite samples. Dissolving even small amounts of fluorite in an acidic solution can be quite corrosive to the skin.

Carbonate (rhombohedral, calcite-like structure) Magnesite MgCO3 (NOT REQUIRED FOR 3rd TEST)

Diagnostic features: no noticeable reaction with room-temperature HCl solution. Habit: crystals are rhombohedral, but good forms are rarely seen. Usually found in compact masses. The shape of

small fragments should reflect the rhombohedral cleavage. Colour: usually white or gray. Hardness: 3.5-5 (varies with crystal size). Look-alikes: anhydrite. Weak reaction to acid may be due to a mixture with calcite or dolomite. Magnesite is quite rare and has two main origins. The first one is hydrothermal alteration of Mg-rich igneous and metamorphic rocks, in which case it is often associated with opaline silica, talc, chlorite or serpentine. The second possibility is by alteration of limestone (CaCO3) in which case it is associated with dolomite.

Carbonate (rhombohedral, calcite structure) Dolomite CaMg(CO3) 2 Diagnostic features: rhombohedral cleavage, little reaction with HCl at room temperature (more soluble if the

mineral is powdered), often slightly rusty on weathered surface. Habit: unit rhombohedra are common, sometimes with curved faces (“saddle” dolomite, shown to the right, below).

Perfect rhombohedral cleavage like calcite and other rhombohedral carbonates. Polysynthetic twinning is common, giving rise to striations along the long diagonal of the rhombic faces.

Colour: white or in shades of flesh or pink. Hardness: 3.5-4. Look-alikes: Siderite. Ankerite, CaFe(CO3)2, is the name given to Fe-rich varieties of dolomite that are intermediate

in properties and compositioin between dolomite and siderite. Ankerit is typically yellowish to yellowish-brown, with a weak reaction to HCl similar to that of dolomite.

Carbonate (rhombohedral, calcite structure) Siderite FeCO3 Diagnostic features: rhombohedral cleavage, brown colour, vitreous luster, moderate hardness (H = 3.5-4). Should

barely react to HCl at room temperature. Habit: crystals are usually simple unit rhombohedra, often with curved faces. Also occurs in compact, granular

masses. Perfect rhombohedral cleavage. Colour: light to dark brown. Vitreous luster. Hardness: 3.5-4. Look-alikes: Dolomite, ankerite. Siderite is associated with some coal beds and metallic ore deposits of hydrothermal origin. It has been mined as an ore of iron in Europe.

Carbonate (rhombohedral, calcite structure) Rhodochrosite MnCO3 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: pink colour, rhombohedral cleavage, moderate hardness (H = 4). Weak reaction to room

temperature HCl solution. Habit: rhombohedral and scalenohedral crystals are rare. Usually in cleavable compact masses, often banded. Colour: usually pink (characteristic), though the shade may vary from light pink to red or dark brown.. Look-alikes: Dolomite. Rhodochrosite is a relatively rare hydrothermal vein mineral.

carbonate (rhombohedral) Calcite CaCO3

Diagnostic features: noticeable reaction (effervescence) with HCl at room temperature, rhombohedral cleavage, moderate hardness (H = 3-3.5). Habit: highly variable but a three-fold or six-fold symmetry is often clearly visible. Crystals can be nearly acicular or flattened plates. Most are combinations of rhombohedra and prism(s) or scalenohedra.. Colour: colourless when pure, but highly variable because of the presence of fluid inclusions, organic matter, inclusions of other minerals or substitution of Ca2+ ions by various impurities.

Cleavage fragments of limpid, colourless calcite crystals displays pronounced double refraction. There is no double refraction if one looks through the crystal down its c axis. Calcite and aragonite are polymorphs of calcium carbonate.

Carbonate (rhombohedral, calcite structure) Smithsonite ZnCO3 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: botryoidal habit, slightly harder (H = 4-4.5) than some other carbonates, weak or no reaction to

HCl at room temperature. Habit: single crystals (rhombohedral or scalenohedral, below and to the right), are rare. Aggregates are usually

reniform (below, to the left), botryoidal or stalactitic. Colour: light green to dirty brown (but we have lilac-coloured specimens in the teaching collection). Smithsonite is a zinc ore formed by the alteration of sphalerite (ZnS) by carbonated hydrothermal waters. It is commonly associated with sphalerite, galena, cerussite, calcite and limonite (the amorphous form of goethite). Look-alike: Prehnite forms similar-looking crusts but it is not associated with zinc or lead sulfides.

Sulfate Gypsum CaSO4 • 2 H2O Diagnostic features: low hardness (H = 2, scratched by fingernail), planes of cleavage forming rhombic plates. Habit: well-formed crystals are tabular, with a rhombic outline (1st picture). They sometimes grow as ‘swallowtail’

twins (see 2nd picture below). Colour: white, colourless or lightly coloured by impurities (pale shades of yellow, red and brown). Vitreous luster. Selenite is the name given to perfectly transparent gypsum. Satin spar is a fibrous variety with silky luster. Alabaster is a fine-grained massive variety used as an ornamental stone. "Plaster of Paris", the material used as wallboard in the building industry, is obtained by heating gypsum until 3/4 of its water has been driven out. Look-alikes: none.

Sulfate Barite BaSO4

Diagnostic features: noticeably high specific gravity (G = 6.55) for a non-metallic mineral, good cleavage. Habit: single crystals are generally tabular, often with a rhombic cross section. Cleavage: an excellent basal (001) cleavage and a good prismatic (210) cleavage with rhombic cross section. The

basal cleavage is perpendicular to the rhombic cleavage so fragments break into plates with rhombic outlines .

Hardness: 3 - 3.5 Colour: often white but can be coloured by many impurities. Look-alikes: difficult to distinguish in hand specimens from witherite and celestine, two other less common sulfates with a similar structure and physical properties. Barite typically forms in hydrothermal conditions, i.e. it precipitates from hot underground waters, and is often associated with fluorite and calcite (or other rhombohedral carbonates).

Sulfate Anhydrite CaSO4 Diagnostic features: three cleavage at right angles (pseudo-cubic), softer than fluorite (3-3.5). Habit: orthorhombic, but large single crystals are rare. In aggregates, the thick tabular habit and three perfect to good

cleavage of crystals can give the appearance of an isometric mineral. Cleavage: {010} perfect, {100} nearly perfect, and {001} good. Colour: colorless, white, or tinged with pink, bluish, brown, etc. Luster is vitreous to pearly on cleavage surfaces. Hardness: 3-3.5 Look-alikes: halite (softer, water soluble), magnesite (rhombohedral cleavage), massive gypsum (usually softer).

Less common than gypsum. Usually formed from evaporation of inland seas. Can be redeposited into cavities and veins during deep burial of sedimentary rocks. Sometimes found with calcite (in which case you should notice effervescence with dilute HCl between the anhydrite crystals).

Sulfate Celestite SrSO4 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: light blue colour (common but not necessarily diagnostic ) and high specific gravity. Habit: single crystals are generally tabular, often with a rhombic cross section. Cleavage: an excellent basal (001) cleavage and a good prismatic (210) cleavage with rhombic cross section. The

basal cleavage is perpendicular to the rhombic cleavage so fragments break as plates with rhombic outlines .

Colour: commonly tinted pale blue or yellow but can also be white. Hardness: 3 - 3.5 Look-alikes: Barite and anglesite which have a similar structure and physical properties.

Usually of hydrothermal origin, commonly found with calcite, dolomite, gypsum or fluorite. Celestite and barite are so similar that you cannot be sure to tell them apart without a chemicalor X-ray diffraction analysis. Barite is far more common, however.

Sulfate Anglesite PbSO4 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: very high specific gravity (G = 6.2-6.5 is even higher than barite's 4.5). Habit: variable, but commonly similar to barite (tabular, often with a rhombic cross section). Cleavage: an excellent basal (001) cleavage and a good prismatic (210) cleavage with rhombic cross section, as in

barite. Colour: colourless, white, grey or pale shades of yellow, Hardness: 3 Look-alikes: Barite and celestite, who share the same structure. Forms by oxidation of a primary Pb sulfide, usually galena. Usually found as a crust (possibly with cerussite) on galena. Might occur with smithsonite and iron oxides forming the corresponding oxidized crusts on sphalerite.

carbonate Malachite Cu2CO3(OH)2 Diagnostic features: green colour, moderate hardness, effervesces when in contact with HCl. Habit: single crystals (below, left) are usually indistinct. Botryoidal masses (below, center) of radiating fibers are

common, often showing concentric banding (below, right) on cut surfaces. Colour: green. Streak: pale green. Luster: vitreous, silky or dull, depending on the crystal size. Hardness: 3.5-4 (easily scratched by a knife). Look-alike: Chrysocolla (a silicate which does not effervesce). This mineral tends to form near the Earth's surface, by weathering and the action of carbonated water (acid rain) on copper sulfide minerals such as chalcopyrite. It is often associated with blue azurite, Cu3(CO3)2(OH)2.

The colour banding of malachite (seen on the right) represents successive epsidoes of growth from hydrothermal fluids, in veins and in the oxidized zone of copper deposits.

Carbonate Azurite Cu3(CO3)2(OH)2 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: blue colour, moderate hardness, effervesces when in contact with HCl. Habit: single crystals are rare. Botryoidal masses of radiating crystals are common. Colour: blue. Streak: pale blue. Luster: vitreous, silky or dull, depending on the crystal size. Hardness: 3.5-4 (easily scratched by a knife). Look-alikes: none among the minerals seen this term. This mineral tends to form near the Earth's surface, by weathering and the action of carbonated water (acid rain) on copper sulfide minerals. It is less common than green malachite, Cu2CO3(OH)2, but it has the same origin and is often associated with it.

Tungstate Wolframite (Fe, Mn)WO4 (NOT REQUIRED FOR 3rd TEST) Diagnostic features: submetallic luster, bladed habit, high specific gravity, nearly black to brown streak. Habit: monoclinic crystals are usually tabular to bladed. Single perfect cleavage in (010) direction. Colour: brown to black (increases with Fe content). Luster: submetallic to resinous (as in sphalerite). Streak: nearly

black to brown (darker than that of sphalerite). Hardness: 4.5-5.5 Look-alikes: iron-rich varieties of sphalerite, ilmenite, chromite. Found in pegmatites and high-temperature quartz veins associated with granites. More rarely in sulfide veins. Associated with quartz or primary sulfides (galena, sphalerite and arsenopyrite) rather than secondary or low-temperature sulfides (such as marcasite).

Arsenate Erythrite Co3(AsO4) 2 · 8H2O (NOT REQUIRED FOR 3rd TEST) Diagnostic features: crust-like habit, pink colour, and association with cobalt or nickel arsenide minerals (often

skutterudite or cobaltite, (Co,Fe)AsS, a silvery gray pyrite look-alike which oxidizes to erythrite).

Habit: occurs as crusts, globular or reniform, powdery or earthy. Larger crystals are rare but they are typically

slender prismatic blades (shown below). Colour: crimson to pink (erythrite), with a streak of similar colour. Hardness: 1.5-2.5 Look-alikes: fine-grained crusts of cuprite or cinnabar. Distinguished by its mode of occurrence, usually as an alteration of a metallic silvery sulfide or sulfosalts.

Phosphate Apatite Ca5(PO4) 3(F, Cl, OH) Diagnostic features: hexagonal prismatic habit, moderate hardness (H = 5). Habit is similar to beryl but it is soft

enough to be easily scratched by a knife. Habit: well-formed hexagonal prisms are common. Poor cleavage. Fractures perpendicular to length are common.The crystal faces are often corroded by dissolution following crystallization. Colour: variable. Reddish-brown and green are common, sometimes in the same crystal. Hardness: 5 (scratched by knife but not by fingernail). Look-alikes: other hexagonal prismatic minerals such as beryl, tourmaline or corundum are much harder. This fairly common mineral is found as accessory in igneous rocks, metamorphic rocks and hydrothermal deposits. It also makes up most of your bones and teeth. The fluorine-rich apatite (fluorapatite) is noticeably harder and more resistant to dissolution by acid than the other two. This is why the fluoridation of water and toothpaste is generally considered to contribute to dental health.

Arsenate Annabergite Ni3(AsO4) 2 · 8H2O Diagnostic features: crust-like habit, green colour, association with nickel arsenide minerals (such as nickeline). Habit: occurs as crusts, globular or reniform, powdery or earthy. Colour: deep to pale green (the colour is paler when the crystal size is very small). Hardness: 1.5-2.5