practical prospector's guide to minerals

PRACTICAL PROSPECTOR'S GUIDE TO MINERALS[ ] October 3, 2012

HZH, Tanta Univ

PRACTICAL PROSPECTOR'S GUIDE TO

MINERALS

By

Prof. Dr. Hassan Z. Harraz

Geology Department

Faculty Sciences, Tanta University-Egypt

[email protected]

Outline

Topic 1:Rock-Forming Minerals

Topic 2:Ores (Metallic)

Topic 3:Ores (NON-Metallic)

Topic 4:Industrial Minerals

Topic 5:Gem Minerals

mailto:[email protected]


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PRACTICAL PROSPECTOR'S GUIDE TO

MINERALS

I- Rock-Forming Minerals

Quartz

Most common mineral species

Vitreous luster; conchoidal fracture; hexagonal, prismatic crystals are

diagnostic

Many color varieties: amethyst, smoky, rose, citrine

Uses: glass manufacture, abrasive, flux, optical instruments,

electronics

Feldspar Group

Potassium feldspars: microcline, orthoclase, sanidine

blocky crystals, often show perthitic texture (especially microcline)

Plagioclase feldspars: albite – anorthite series

range from white to black

often show play of colors (labradorescence)

striations on cleavage surface (albite twinning)

Mica Group

Muscovite (white mica)

Biotite (black mica)

Phlogopite (brown mica)

Sericite (brown to buff mica)

Lepidolite (purple mica)

lithium-rich pegmatites

micaceous cleavage, elastic nature of plates and hardness distinguish

micas from all other sheet-like minerals such as talc, gypsum and

brucite

Pyroxene Group

Generally green to black (except spodumene, which can be white,

yellowish, pink or green).

2 good to perfect cleavages at nearly right angles (chief distinguishing

characteristic between pyroxenes and amphiboles).

Pyroxenes are common in mafic to ultramafic rocks and in skarns

Emerald-green diopside (chrome-diopside) is a diamond indicator

mineral

Spodumene is a lithium pyroxene found in rare-element pegmatites

Jadeite is one of the "true" jades and is a pyroxene

Amphibole Group

• Generally green to black (some, like tremolite, are white)


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2 good to perfect cleavages at 56 and 124 degrees (chief

distinguishing

characteristic between amphiboles and pyroxenes).

BC jade is "nephrite", a variety actinolite, and is considered a "true"

jade.

amphiboles are common in skarns and in fairly high-grade

metamorphic rocks.

Garnet Group

Almandine (iron – aluminum garnet)

generally red

found in schists

Pyrope (magnesium – aluminum garnet)

generally red

diamond indicator mineral (kimberlites, lamprophyres)

Spessartine (manganese – aluminum garnet)

red to orange

most often in rare-element pegmatites

Grossular (calcium – aluminum garnet)

brown, green, red, yellow

often found in skarns

gem brown variety known as "hessonite"

Andradite (calcium – iron garnet)

brown, green, red, yellow, black

often found in skarns

gem green variety could be "demantoid"

titaniferous variety (black) is known as "melanite"

Uvarovite (calcium – chromium garnet)

chrome green

associated with altered ultramafic rocks.

Serpentine Group

varied green color, greasy luster, often fibrous (or splintery)

Olivine

vitreous luster, conchoidal fracture, green color, presence in basalt as

nodules

Carbonate Group

Calcite

3 cleavages not at right angles

fizzes readily with weak acid

Siderite

typical carbonate cleavage

light to dark brown

Dolomite

curved, rhombohedral crystals

white, pink, gray


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II- Ores (Metallic)

A. Gold

B. Platinum Group Elements:

Platinum, Palladium, Iridium, Osmium

placer deposits, ultramafic rocks

C. Native Silver

wires in pockets, hackly fracture, tarnishes black

often as an impurity in galena

D. Sulfosalts

Pyrargyrite/Proustite (ruby silvers)

Stephanite

Tetrahedrite

E. Native Copper (100% Cu)

often in basalt; sometimes in oxidized zone; hackly fracture,

copper color

F. Chalcopyrite (35% Cu)

no cleavage, greenish-black streak, slightly greener yellow than

pyrite

G. Bornite (63% Cu)

purple-blue iridescent tarnish, BRONZY on FRESH

SURFACE

H. Covellite (66% Cu)

ELECTRIC BLUE, platy cleavage

I. Chalcocite (79% Cu)

black, SECTILE

J. Galena

3 perfect CLEAVAGES at right angles, DENSITY, lead-gray

color

secondary lead minerals: anglesite, cerussite, pyromorphite

J. Molybdenite

chief ore of molybdenum

SOFT, slightly bluer-gray than graphite (compare it with a

pencil ‘lead’)

L. Pyrite

often in good crystals (pyritohedra, cubes, octahedra); brittle,

black streak

M. Arsenopyrite

no cleavage, "garlic" smell sometimes when broken

N. Pyrrhotite

bronzy color, sometimes magnetic

O. Stibnite

main ore of antimony.

elongate crystals that are often ‘bent’; ONE PERFECT

CLEAVAGE and lower density distinguish it from galena.

will easily melt in a candle flame

P. Graphite

SOFT, black (like pencil "lead")


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III- Ores (NON-Metallic) A. Sphalerite

resinous to sub-metallic luster

yellow to green to red to black

Important ore of cadmium as well

alters to smithsonite, hydrozincite (fluorescent)

B. Wolframite

HEAVY, reddish to black, tabular crystals with one perfect

cleavage

C. Scheelite

White to brown, fluoresces bluish white

D. Manganese Oxides

psilomelane is a mixture of compact manganese oxides;

mixture of earthy manganese oxides is known as wad.

black, soft (often show dendritic stains)

E. Iron Oxides

mixture of iron oxides is generally known as limonite

1. Hematite: red-brown streak

2. Goethite: brown streak

F. Magnetite

black, dense, MAGNETIC

G. Cassiterite

black; glassy to resinous luster

H. Cinnabar

red; bright red streak; soft

I. Cuprite

red, often associated with malachite or other secondary copper

minerals

J. Malachite/Azurite

both are alteration products of other copper minerals

(MALACHITE is GREEN; AZURITE is BLUE (‘azure-blue’,

in fact)


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IV- Industrial Minerals Diamond

as adamantine crystals in kimberlite or lamprophyre

placer deposits (weathered kimberlites/lamprophyres)

Sulfur

as a native element in sedimentary rocks (often associated with

petroleum)

Barite

one to two good cleavages, VERY heavy

in hydrothermal veins and sedimentary exhalative deposits

Gypsum

white to gray, softness is characteristic

sedimentary rocks

Magnesite

generally white

found most commonly in sedimentary rocks, but also in

carbonatites

hydromagnesite and epsomite are evaporites found in playa

lakes (from the alteration of volcanic rocks)

Apatite

hexagonal crystals, many colors

found in many environments

distinguished from beryl by its hardness (beryl cannot be

scratched by a knife)

Zeolite Group

generally white or off-white

found in volcanic rocks or low grade metamorphic rocks

economic deposits found as beds of altered volcanic ash

"boil" when torched

Fluorite

four directions of perfect CLEAVAGE

Corundum

HARDNESS of 9


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V- Gem Minerals The following are reasonable to be expected, or have already been found in British

Columbia.

Corundum

Ruby: red corundum coloured by chromium

Sapphire: BLUE, green, pink, yellow, colourless corundum coloured

by iron and/or titanium

Diamond

Beryl

hexagonal cross-section; prismatic to tabular crystals; generally in

pegmatites

Varieties of Beryl:

Aquamarine: blue to green beryl coloured by iron

Emerald: green beryl coloured by chromium or vanadium

Goschenite: colourless beryl (originally cesium-bearing beryl)

Heliodor: yellow beryl coloured by iron

Tourmaline

diamond-shape cross-section; perfect basal cleavage (perpendicular to

the length of the crystal)

Varieties of Gemmy Tourmaline:

Schorl: black tourmaline found in simple pegmatites, hydrothermal

veins and metamorphic rocks

Elbaite: lithium-bearing tourmaline found almost exclusively in

pegmatites;

Rubellite (pink), Verdelite (green), Indicolite (blue), Achroite

(colourless)

Liddicoatite: another lithium-bearing tourmaline, again in pegmatites

Topaz

diamond-shape cross-section; perfect basal cleavage (perpendicular to

the length of the crystal)

Garnet

metamorphic rocks; pegmatites

Varieties of Gemmy Garnet:

Grossular: gem brown variety is hessonite

Andradite: gem green variety is demantoid

Spessartine: bright orange is best quality

Quartz

Varieties of Quartz:

Amethyst: purple quartz coloured by iron (Fe4+)

Citrine: yellow/orange quartz coloured by iron

Smoky Quartz: brown to black quartz affected by radiation

Rose Quartz: pink quartz coloured by manganese


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Chalcedony: cryptocrystalline quartz; gray, greasy to silky luster;

found in volcanic rocks and some sedimentary rocks

Agate: concentrically banded chalcedony; variously coloured

Onyx: flat, layered chalcedony; usually black/white or red/white<

Carnelian: chalcedony coloured red by iron

Chrysoprase: chalcedony coloured green by nickel

Jasper: chalcedony coloured red, green, yellow or black by iron oxide

Opal

in volcanic and sedimentary rocks

common versus precious opal

practical prospector's guide to minerals

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