Mineral Groups - geo1stsem2012

Mineral Groups

Mineral Groups

Element Abundances

SILICATES

All others: 1.5%

Common cations that bond with silica anions

Silica

(SiO

4

) 4-

Mineral Groups

Non-ferromagnesian

Silicates (K, Na, Ca, Al)

Ferromagnesian

Silicates (Fe, Mg)

Oxides

Carbonates

Sulfides/sulfates

Native elements

Silicates

Actinolite (Tremolite) Ca

Subclass: Amphibole

2

(Mg,Fe)

5

Si

Streak: White

8

O

22

(OH)

2

Lustre: Vitreous Hardness: 5 – 6

Density: 3.0 - 3.4

Habit: Aggregate of acicular grains

Colours: Greenish - white

Crystal System: Monoclinic

Cleavage: Uneven

Fracture: Subconchoidal

Magnetism: None

Reaction with HCl: None

Identification in hand sample:

Habit and colour are best indicators.

Associations:

Metamorphosed calcareous sediments

Comments:

Higher in Fe than tremolite.

Silicates

Antigorite (Serpentine) Mg

3

Subclass: Phyllosilicate

Hardness: 2.5 - 3.5

Density: 2.6

Habit: Lath-shaped crystals.

Colours: Shades of green

Si

2

O

5

(OH)

4

Streak: White

Lustre: Greasy or waxy


Cleavage: Perfect basal

Fracture: Splintery or conchoidal

Magnetism: None

Reaction with HCl: Unknown


Lustre, colour and habit are indicative.

Associations:

Formed by hydrothermal action of mafics and ultramafics. Associations may include talc, calcite, brucite, chlorite, magnetite and chromite.

Silicates

Augite (Ca,Na)(Mg,Fe,Al,Ti)(SiAl)

2

O

6

Subclass: Pyroxene

Hardness: 5.5 – 6

Density: 3.2 - 3.5

Habit: Small blocky grains.

Colours: Dark-greeny black colour

Streak: White or gray

Lustre: Vitreous


Cleavage: Good / Uneven

Fracture: Uneven to conchoidal

Magnetism: None



Colour, cleavage and hardness are indicative of a pyroxene. Augite has 2 cleavage planes at 90°.

Associations:

Found in mafic to ultramafic rocks, and in high-grade metamorphs.

Industrial / ecomonic uses:

None.

Silicates

Biotite K(Mg,Fe)

3


(AlSi

3

O

10

)(OH)

2

Hardness: 2 – 3

Density: 2.7 - 3.4

Habit: Micaceous

Colours: Brown, black, reddish brown

Streak: Colourless




Fracture: Uneven

Magnetism: None

Reaction with HCl: Very weak


Colour and habit

Associations:

A very common mineral found in igneous, metamorphic and sedimentary rocks.


Altered into vermiculite, biotite is used as an insulation material and as filler in certain building supplies.

Silicates

Chalcedony (Micro/Cryptocrystalline Quartz) -- SiO

Subclass: Framework

Hardness: 7

Density: 2.7

Streak: White

Lustre: Vitreous / almost waxy

Habit: Aggregate of very tiny SiO

2

Colours: White/gray or any colour grains.

2

Crystal System: Hexagonal

Cleavage: None

Fracture: Conchoidal

Magnetism: None



Identified by hardness and texture/habit.

Associations:

Abundant in felsic rocks.


Used for making glass and as a source of Silicon.

Silicates

Chlorite (Mg,Fe,Al)

3

(Si,Al)

4

O

10

(OH)

2


Hardness: 2 - 2.5

Density: 2.6 - 3.3

Streak: Greenish white to white

Lustre: Vitreous to somewhat pearly, waxy, dull

Colours: Greenish-black (typical)


Cleavage: Perfect {001}

Magnetism: None



Colour and its low hardness are distinguishing characteristics.


None, however chlorite schist sometimes does have ornamental uses.

Silicates

Chrysotile (Serpentine) Mg

3


Si

2

O

5

(OH)

4

Hardness: 2.5

Streak: White

Lustre: Silky Density: 2.5

Habit: Fibrous

Colours: Shades of green


Cleavage: None


Magnetism: None



Habit and colour and most indicative properties.

Associations:

Found by hydrothermal alteration of mafics and ultramafics. Associated with talc, calcite, brucite, chlorite, magnetite and chromite.


Used in 98% of world's production of asbestos.

Silicates

Epidote Ca

Subclass: Sorosilicate

2

(Fe,Al)

3

(SiO

4

)

3

(OH)


Density: 3.4 - 3.5

Streak: White


Habit: Aggregate of small grains, striated faces, small but visible crystals

Colours: Greeny, yellow-green, black


Cleavage: Perfect


Magnetism: None



Slight colour difference between this mineral and olivine, but only under magnification (where details in the crystals can be seen). Also indicitive is the presence of a cleavage plane.

Associations:

Common accessory mineral in many regional and contact metamorphed rocks, particularly in more iron-rich rocks.


Semiprecious gemstone

Silicates

Garnet (Pyrope, Grossular,

Almandine)(Mg,Fe,Ca)

3

Hardness: 6.5 – 7

Density: 3.8

Habit: Small, well-formed crystals

Colours: Darker reddy colours

Al

2

(SiO

4

)

3

Streak: White


Crystal System: Isometric

Cleavage: None


Magnetism: None



Crystal habit, colour and hardness.


Abrasives (particularly sandpaper), semi-precious gemstone.

Silicates

HornblendeCa

2

(Mg,Fe)

4

Al(Si

7

Al)O

22

(OH,F)

2

Subclass: Amphibole

Hardness: 5 – 6 Streak: White or gray

Density: 3.3 - 3.4


Habit: Intergrown crystals, prismatic character of grains.

Colours: Black


Cleavage: 2 at 56° and 124°

Fracture: Uneven / conchoidal

Magnetism: None



Prominent striations, prismatic crystals and angle on cleavages is distinguishing.

Associations:

Forms in igneous rocks, and in the metamorphic rock amphibolite.

Industrial / ecomonic uses: Ornamental.

Silicates

Muscovite KAl

2

(AlSi

3

O

10

)(OH)

2


Hardness: 2.5 – 4

Density: 2.8 - 2.9

Habit: Micaceous

Colours: Colourless, to white or gray

Streak: Colourless





Magnetism: None



Colour and habit are best indicators.


Used in the electronics industry in the manufacture of capacitors, transistors, insulators and certain window types. Also used as a filler in building materials.

Silicates

Olivine (Forsterite (Mg) and Fayalite (Fe))Mg

2

Subclass: Nesosilicate

SiO

4

Hardness: 6.5 – 7 Streak: Colourless

Density: 3.3 - 4.3

Habit: Granular


Colours: Pistachio green, greenish yellow brown

Crystal System: Orthorhombic

Cleavage: Imperfect


Magnetism: None


- Fe

2

SiO

4


Pistachio-green colour and granular habit.

Associations:

Mafic and ultramafic igneous rocks. Associated with Ca-plag,


Peridote (a translucent variety of olivine) is considered a 'gem' mineral. Also used as a refractory sand and infrequently as an abrasive.

Silicates

Orthoclase KAlSi

3

O

8

Hardness: 6 - 6.5

Density: 2.6

Habit: Polysynthetic twinning

Colours: Pinky-white




Magnetism: None


Streak: White



Colour and evidence of exsolution with plagioclase.

Associations:

Very common in granite, granodiorite, syenite and related felsic rocks.

Silicates

Quartz (crystal) SiO

2

Hardness: 7

Density: 2.7

Lustre: Vitreous / glassy

Habit: Crystalline

Colours: Clear transparent


Cleavage: None


Magnetism: None



Hardness, translucency and colour are indicators.

Silicates

Talc Mg

Hardness: 1

3

Si

Density: 2.6 - 2.8

4

O

10

Subclass: Phyllosilicate

(OH)

2

Streak: White

Lustre: Greasy

Habit: Compact masses, often no crystals.

Colours: White, or brownish, dark green, gray

Crystal System: Monoclinic

Cleavage: Perfect

Fracture: Uneven

Magnetism: None

Reaction with HCl: Unknown

Identification in hand sample:

Mineral is very soft and are often compact masses. Colour is typical and varies to brown, green or gray.

Silicates

Topaz Al

2

Hardness: 8

Density: 3.5

SiO

4

(F,OH)

2

Streak: White

Lustre: Glassy

Habit: Prismatic crystals

Colours: Almost brownish, any colour




Magnetism: None



Resembles quartz, but harder.

Associations:

Quartz


Gemstone

Silicates

Zircon (ZrSiO

4

)

Hardness: 7.5

Density: 4.6 - 4.7

Streak: White

Lustre: Subadamantine

Habit: Excellent tetragonal prisms

Colours: Colorless, red, brown, yellow, green or gray

Crystal System: Tetragonal

Cleavage: Imperfect


Magnetism: None



Excellent crystalline habit, density and streak/colour are indicative.


Source of zirconium and hafnium

Carbonates

Azurite ---Cu

3

(CO

3

)

2

(OH)

2

Hardness: 3.5 – 4

Density: 3.8

Streak: Lighter blue

Lustre: Vitreous, earthy (fine grained)

Habit: Fine grained coating or fracture filling on rock

Colours: Azure blue




Magnetism: None

Reaction with HCl: Strong


Colour is reliable, association with malachite is also indicative.

Associations:

Common mineral in the near-surface oxidized portion of copper-bearing hydrothermal sulfide mineral deposits. Associated with malachite.


A minor ore of copper, also has ornamental uses. Sometimes a pigment (when powdered).

Carbonates

Aragonite ----CaCO

3

Hardness: 3.5 – 4

Streak: White

Colours: Colourless or white


Habit: Stalactitic aggregate of crystals or grains.


Cleavage: Pinacoidal


Magnetism: None



Stalactitic habit, hardness (greater than that of calcite) and colour.

Associations:

Occurs in carbonate-bearing blueschist metamorphic rocks. Associated with glaucophane, lawsonite, pumpellyite. Also forms at or near the surface in cave and hot spring deposits.


Same as calcite, however abundance is much much less than that of calcite, thus having little economic value.

Carbonates

Calcite (massive) CaCO

3

Hardness: 3 Density: 2.7

Streak: White Lustre: Vitreous

Habit: Fine grained aggregates (massive)

Colours: Colourless, white, gray, yellow-brown, pink, rose red


Cleavage: Perfect rhombohedral


Magnetism: None



Recognized by hardness and cleavage. Dolomite and aragonite have higher densities.

Associations:

Common as a cementing agent in clastic sediments, or as fossil fragments. Essential constituent of limestone.


Used in the manufacture of portland cement (quicklime). Also used as a pharmaceutical (antacids, calcium supplements).

Carbonates

Calcite (sparry) (Iceland Spar) ---- CaCO

3

Hardness: 3 Streak: White

Density: 2.7


Habit: Large crystals, some exhibiting common twin striae

Colours: White




Magnetism: None



Hardness, crystal habit and twin striae are typical.

Associations:

Common as a cementing agent in clastic sediments or as fossil fragments.


Used in the manufacture of portland cement (quicklime) and in the pharmaceutical industry.

Comments:

The transparent variety is called "Iceland Spar".

Carbonates

Dolomite ---- CaMg(CO

Hardness: 3.5 – 4

3

Streak: White

)

2

Density: 2.85


Habit: Crystalline or aggregate, some with twin striae.

Colours: Pinky/peach, white, gray, brown.




Magnetism: None

Reaction with HCl: Weak


Harder than calcite

Associations:

Major constituent of dolostone (aka dolomite).


Used in manufacture of portland cement.

Carbonates

Malachite ---Cu

Hardness: 3.5 – 4

2

(CO)

3

(OH)

Streak: Pale green

2

Density: 4.0

Lustre: Earthy

Habit: Very fine grained coating on other rocks, almost looks like paint.

Colours: Copper green




Magnetism: None



Colour is primary indicator, as well as habit.

Associations:

Common in near-surface oxidized portions of copper bearing hydrothermal sulfide mineral deposits.


Used as a minor ore of copper and also has ornamental uses due to vivid green colour.

Carbonates

Siderite ---- FeCO

3

Hardness: 3.5 – 4

Density: 4.0

Habit: Aggregate of crystals or grains

Colours: Tan brown (typical)

Streak: White





Magnetism: None



Identified by colour and hardness.

Associations:

Produced by hydrothermal alteration of limestone. May also occur as concretionary or oolitic forms in clay ironstones.


Sometimes used as an iron ore. Also used in pigments where a red or brown colour is desirable.

Halides

Fluorite --- CaF

2

Hardness: 4

Density: 3.1 - 3.3

Streak: White


Habit: Crystals, usually cubic

Colours: Commonly colourless, blue, purple or green, but any is possible.


Cleavage: Perfect octahedral


Magnetism: None



Cubic crystals, hardness and colour indicative.

Associations:

Common in hydrothermal mineral deposits associated with sulfides, carbonates and barite.


Main source of fluorine (which is added to drinking water, toothpaste, used as a flux in industrial uses and as part of CFCs)

Halides

Halite (Salt) --- NaCl

Hardness: 2

Density: 2.1 - 2.2

Streak: White

Lustre: Waxy

Habit: Crystalline (cubic)

Colours: Colourless or white if pure, any colour if not


Cleavage: Cubic


Magnetism: None



Has a salty taste. Cubic cleavage and hardness are indicative for the less brave geologists.

Associations:

Abundant in marine evaporite deposits and may form beds hundreds to over a thousand meters thick. Associated minerals include calcite, dolomite, gypsum, anhydrite and sylvite.

Hydroxide

Limonite-- FeO(OH)

Hardness: 5 - 5.5

Density: 2.7 - 4.3

Streak: Yellow-brown

Lustre: Earthy

Habit: Fine grained aggregate, powdery coating.

Colours: Orange, yellow-brown

Crystal System: Unknown

Cleavage: None


Magnetism: None



Colour is best indicator, followed by habit.

Associations:

Common weathering product of iron-rich rocks.

Comments:

The fine brownish coloured mineral is usually weathered goethite.

Oxides

Chromite (FeCr

2

Hardness: 5.5

O

4

)

Density: 4.5 - 4.8

Streak: Brown

Lustre: Metallic to pitchy

Habit: Fine grained aggregate.

Colours: Black


Cleavage: None


Magnetism: Weak



Resembles magnetite and ilmenite, but not very magnetic and has a more resinous lustre.

Associations:

Found in mafic and ultramafic igneous rocks such as gabbro, peridotite, dunite and pyroxenite as an accessory mineral.


Only ore mineral for chromium.

Oxides

Corundum (Al

2

Hardness: 9

O

3

)

Density: 4.0 - 4.1

Habit: Well-formed crystals

Streak: White

Lustre: Vitreous to adamantine

Colours: Any. White, gray or gray-blue, or red (ruby), blue (sapphire), yellow, green.


Cleavage: None


Magnetism: None



Hardness is best indicator, crystal habit is good too.

Associations:

Gem quality corundum comes from metamorphed limestone or dolostone (needs high Al concentrations, here presumably from detrital deposits)


Used as a gemstone. High-quality ruby can be more valuable than diamond. Corundum is also used as an abrasive in sandpaper, polishing compounds, etc.

Oxides

Hematite (massive) -- (Fe

2

O

3

)


Density: 5.3

Streak: Deep red

Lustre: Earthy

Habit: Very fine grained aggregate of red crystals.

Colours: Deep red


Cleavage: None


Magnetism: Weak



Deep red streak and earthy lustre are indicative. SG may also be indicative.

Associations:

Produced by weathering or hydrothermal alteration of iron-bearing minerals. May be found in some syenite, trachyte, granite and rhyolite.

Industrial / economic uses:

Important ore or iron, sometimes used as a gemstone.

Comments:

May become magnetic when heated.

Oxides

Hematite (specular) (Fe


Density: 5.3

Streak: Deep red

Lustre: Metallic

Habit: Micaceous/tabular habit.

Colours: Steel gray

2

O

3

)


Cleavage: None


Magnetism: None



Shining gray metallic lustre and deep-red streak are indicative.

Associations:

Produced by weathering and hydrothermal alteration of iron-bearing minerals.


Important ore of iron.

Oxides

Magnetite (Fe

3

Hardness: 5.5 - 6.5

O

4

)

Density: 5.2

Streak: Black

Lustre: Dull metallic to splendent

Habit: Granular habit of fine grains. Some octahedral crystals may form.

Colours: Black


Cleavage: None


Magnetism: Strong



Highly magnetic. Habit and colour are also indicators.

Associations:

Very common accessory mineral found in a wide variety of igneous and metamorphic rocks, usually as small grains.


Mined for iron. Crushed magnetite also been used as aggregate to make high-density concrete for specialized applications, such as nuclear reactors.

Oxides

Pyrolusite (MnO

Hardness: 2 - 6.5

2

)

Streak: Black

Density: 5.1

Lustre: Earthy

Habit: Massive, compact, columnar or fibrous. Prismatic crystals are rare. Sometimes forms as dendritic coatings on other rocks.

Colours: Black




Magnetism: None



Will leave sooty marks if touched.

Associations:

Found in bog and marine deposits


Manganese is used to colour bricks.

Phosphates

Apatite Ca

5

(PO

4

)

3

( OH,F,Cl)

Hardness: 5

Density: 3.1 - 3.2

Streak: White

Lustre: Vitreous, glassy

Habit: Massive

Colours: Grayish blue-green, or any.


Cleavage: Poor


Magnetism: None



Colour, crystal habit and hardness are good indicators.

Associations:

Common accessory mineral in all environments.


Source of phosphate used in fertilizers and other industrial applications. Fluorine is also extractable from apatite.

Comments:

Same stuff as in bones and teeth.

Sulfates

Alabaster (Gypsum) CaSO

4

Hardness: 2 Streak: White

Density: 2.3


Habit: Granular / massive form of gypsum

Colours: Colourless or white (typical)



Fracture: Splintery

Magnetism: None


-

2

H

2

O


Identified by hardness and good cleavage.

Associations:

Common in marine evaporite deposits.


Modern use is in gypsum wallboard used in construction. Used as an ornamental stone and for sculpture due to its softness.

Sulfates

Barite (BaSO

Hardness: 3 - 3.5

4

)

Streak: White

Density: 4.5


Habit: Fine grained aggregates

Colours: Colourless, white, gray, yellowish, brown, reddish, bluish or greenish




Magnetism: None



High specific gravity is best indicator, colour and fracture are also helpful.

Associations:

Common in hydrothermal veins, associated with galena, sphalerite, pyrite, quartz, fluorite and carbonates.


Primary ore for barium, also used as an additive to drilling mud (because of high SG). Has over 2000 uses in industry.

Sulfates

Selenite (Gypsum) CaSO

4

Hardness: 2

Density: 2.3

Streak: White


Habit: Large crystalline habit

Colours: Colourless, clear

-



Fracture: Splintery

Magnetism: None


2

H

2

O


Single large crystals of gypsum, typified by hardness and transparency.

Associations:

Found in marine evaporites.


Used in gypsum wallboard.

Sulfides

Chalcocite (Cu

2

Hardness: 2.5 – 3

Density: 5.5 - 5.8

S)

Streak: Blackish lead-gray

Lustre: Dull metallic

Habit: Chunky fracture, massive habit.

Colours: Blackish lead-gray


Cleavage: Indistinct


Magnetism: None



Black colour with sooty appearance on weathered surfaces and sectile character are distinctive. Bronze-yellow on fresh surfaces.

Associations:

Found in the supergene-enriched zone of copper-bearing hydrothermal sulfide deposits.


Mined as a source of copper.

Sulfides

Chalcopyrite (CuFeS

Hardness: 3.5 – 4

2

)

Streak: Greenish black

Density: 4.3 - 4.4


Habit: Fine grained to massive aggregates.

Colours: Brass yellow, may be tarnished and iridescent.


Cleavage: Poor


Magnetism: None



Distinctive brassy-green colour. Has a richer yellow colour than pyrite and a lower hardness.

Associations:

Most common copper-bearing mineral, found in many hydrothermal sulfide deposits.

Often associated with galena, sphalerite, pyrite and other sulfides.


Mined for its copper which has innumerable industrial uses.

Sulfides

Galena (PbS)

Hardness: 2.5

Density: 7.6

Streak: Lead gray


Habit: Excellent cubic cleavage, crystals usually very evident

Colours: Lead gray


Cleavage: Perfect cubic


Magnetism: None



Gives off a rotten-egg smell in HCl, very high SG, very metallic lustre.

Associations:

Very common in hydrothermal sulfide deposits. Associated with sphalerite, pyrite, chalcopyrite, quartz, calcite, fluorite, and/or barite.


Main ore from which lead is extracted, also a source of silver.

Sulfides

Pyrite (crystalline) FeS

2

Hardness: 6 - 6.5

Density: 5.0

Streak: Greenish/brownish black

Colours: Bronze-yellow


Cleavage: Good


Magnetism: Unknown



Habit: Perfect cubic crystalline habit.


Colour, hardness, streak and habit are best indicators. Gives off sparks when struck with a hard metal object.

Associations:

Most common sulfide mineral, almost always present in hydrothermal deposits.


May be used as source of iron or sulfur, but not normally of economic value.

Sulfides

Stibnite (Sb

2

Hardness: 2

S

3

)

Density: 4.6 - 4.7

Streak: Lead gray


Habit: Range from fine to medium grains to prismatic crystals (with longitudinal striations).

Complex terminations, radiating acicular groups.

Colours: Lead gray, black, iridescent tarnish




Magnetism: None



Colour and small subhedral crystals are indicators. Also rather soft.

Associations:

Forms in low-temperature hydrothermal veins, or is deposited from hot mineral springs.


Important source of antimony (Sb)

Native Elements

Copper (Cu)

Hardness: 2.5 - 3

Density: 8.9

Streak: Same


Habit: Massive, platey or dendritic habit.

Colours: Light rose on fresh surface, copper-red on tarnished surface


Cleavage: None

Fracture: Hackly

Magnetism: None



Colour and metallic characteristics are diagnostic.

Associations:

Found associated with mafic volcanic rocks, formed by reaction between Cu-bearing solutions and Febearing minerals. Associated minerals are cuprite, chalcocite, bornite, epidote, calcite, chlorite and zeolites.


Used as electrical wire due to electrical conductivity and relatively low price.

Comments:

Obviously a source of copper, however most copper in modern times is mined from sulfide minerals.

Native Elements

Graphite (C)


Density: 2.1 - 2.3

Habit: Fine grained aggregate

Colours: Silver-black




Magnetism: None


Streak: Black

Lustre: Dull metallic, greasy feel


Softness and lustre are best indicators.

Associations:

Common in pelitic metamorphic rocks such as phyllite, slate and schist. Produced as a result of decomposition of organic material.


Used in pencil leads and as a dry lubricant.

Comments:

Due to its softness, graphite is usually quite messy!

Reference

Cupit, Kerry. Mineral 1.0. 10June2011. Online. http://www.spaceman.ca/mineral/index.php