Physical Properties of Quartz

Chemical Classificationsilicate

ColorQuartz occurs in virtually every color. Common colors are clear, white, gray, purple, yellow, brown, black, pink, green, red.

Streakcolorless (harder than the streak plate)

Lustervitreous

Diaphaneitytransparent to translucent

Cleavagenone - typically breaks with a conchoidal fracture

Mohs Hardness7

Specific Gravity2.6 to 2.7

Diagnostic Propertiesconchoidal fracture, glassy luster, hardness

Chemical CompositionSiO2

Crystal Systemhexagonal

Usesglass making, abrasive, foundry sand, hydraulic fracturing proppant, gemstones

Physical Properties of Hematite

Chemical Classificationoxide

Colorblack to steel-gray to silver; red to reddish brown to black

Streakred to reddish brown

Lustermetallic, submetallic, earthy

Diaphaneityopaque

Cleavagenone

Mohs Hardness5 to 6 1/2

Specific Gravity5.0 to 5.3

Diagnostic Propertiesred streak, specific gravity

Chemical CompositionFe2O3

Crystal Systemtrigonal

Usesthe most important ore of iron, pigment, heavy media separation, radiation shielding, ballast, polishing compounds, a minor gemstone

Physical Properties of Sulfur

Chemical Classificationnative element

Colorbright yellow

Streakyellow

Lusterresinous

Diaphaneitytransparent to translucent

Cleavagenone

Mohs Hardness1.5 to 2.5

Specific Gravity2.0 to 2.1

Diagnostic Propertiesyellow color, low hardness, low specific gravity, extremely flammable burning with a blue flame, low melting temperature

Chemical CompositionS

Crystal Systemorthorhombic

Usessulfuric acid, fertilizers, insecticides, fungicides, gunpowder, pharmaceuticals, sulfur compounds

Physical Properties of Talc

Chemical Classificationsilicate

Colorgreen, white, gray, brown, colorless

Streakwhite to pale green

Lusterpearly

Diaphaneitytranslucent

Cleavageperfect

Mohs Hardness1

Specific Gravity2.7 to 2.8

Diagnostic Propertiesfeel, color, softness, cleavage

Chemical CompositionMg3Si4O10(OH)2

Crystal Systemmonoclinic

Usesused as a filler and anti-stick coating in plastics, ceramics, paint, paper, roofing, rubber, cosmetics

Physical Properties of Gypsum

Chemical Classificationsulfate

Colorclear, colorless, white, gray, yellow, red, brown

Streakwhite

Lustervitreous, silky, sugary

Diaphaneitytransparent to translucent

Cleavageperfect

Mohs Hardness2

Specific Gravity2.3

Diagnostic Propertiescleavage, specific gravity, low hardness

Chemical Compositionhydrous calcium sulfate, CaSO4.2H2O

Crystal Systemmonoclinic

UsesUse to manufacture dry wall, plaster, joint compound. An agricultural soil treatment.

Physical Properties of Barite

Chemical Classificationsulfate

Colorcolorless, white, light blue, light yellow, light red, light green

Streakwhite

Lustervitreous to pearly

Diaphaneitytransparent to translucent

Cleavagevery good, basal, prismatic

Mohs Hardness2.5 to 3.5

Specific Gravity4.5

Diagnostic Propertieshigh specific gravity, three cleavage directions at right angles

Chemical Compositionbarium sulfate , BaSO4

Crystal Systemorthorhombic

Usesdrilling mud; high density filler for paper, rubber, plastics

Physical Properties of Calcite

Chemical Classificationcarbonate

Colorusually white but also colorless, gray, red, green, blue, yellow, brown, orange

Streakwhite

Lustervitreous

Diaphaneitytransparent to translucent

Cleavageperfect, rhombohedral, three directions

Mohs Hardness3

Specific Gravity2.7

Diagnostic Propertiesrhombohedral cleavage, powdered form effervesces weakly in dilute HCl, curved crystal faces and frequent twinning

Chemical CompositionCaCO3

Crystal Systemhexagonal

Usesacid neutralization, a low hardness abrasive, soil conditioner, heated for the production of lime

Physical Properties of Limonite

Chemical Classificationamorphous, mineraloid

Coloryellowish brown to brown to black

Streakyellowish brown

Lusterdull to earthy

Diaphaneityopaque

Cleavagedoes not cleave because it has an amorphous structure

Mohs Hardness1 to 5 (weathered material can be deceptively soft)

Specific Gravity2.7 to 4.3 (varies due to impurities)

Diagnostic Propertiesvariable - can be yellow-brown, brown, reddish brown

Chemical Compositiona hydrated iron oxide of variable composition

Crystal Systemamorphous to cryptocrystalline

Usesocher pigments, a minor ore of iron

Physical Properties of Magnetite

Chemical Classificationoxide

ColorBlack

StreakBlack

LusterMetallic to submetallic

Diaphaneityopaque

Cleavagenone

Mohs Hardness5.5 to 6.5

Specific Gravity5.2

Diagnostic PropertiesStrongly magnetic, color, streak, octahedral crystal habit

Chemical CompositionFe3O4

Crystal SystemIsometric

Usesan ore of iron

Physical Properties of Galena

Chemical Classificationsulide

Colorfresh surfaces are bright silver in color with a bright metallic luster, tarnishes to a dull lead gray

Streaklead gray to black

Lustermetallic on fresh surfaces, tarnishes dull

Diaphaneityopaque

Cleavageperfect, cubic, three directions at right angles

Mohs Hardness2.5+

Specific Gravity7.4 to 7.6

Diagnostic Propertiescolor, luster, specific gravity, streak, cleavage, cubic or octahedral crystals

Chemical Compositionlead sulfide, PbS

Crystal Systemisometric

Usesan ore of lead

Physical Properties of Halite

Chemical Classificationhalide

Colorcolorless or white when pure; impurities produce any color but usually yellow, gray, black, brown, red

Streakwhite

Lustervitreous

Diaphaneitytransparent to translucent

Cleavageperfect, cubic, three directions at right angles

Mohs Hardness2.5

Specific Gravity2

Diagnostic Propertiescleavage, solubility, salty taste - (The taste test is discouraged. Some minerals are toxic or contaminated by other people tasting them.)

Chemical CompositionNaCl

Crystal Systemisometric

Useswinter road treatment, a source of sodium and chlorine for chemical processes, food preservation, seasoning

Acid Reactions of Carbonate Minerals

What is the Acid Test?To most geologists, the term "acid test" means placing a drop of dilute (5% to 10%) hydrochloric acid on a rock or mineral and watching for bubbles of carbon dioxide gas to be released. The bubbles signal the presence of carbonate minerals such ascalcite,dolomiteor one of the minerals listed in Table 1..

MineralChemical CompositionCold Acid ReactionWarm Acid Reaction

AragoniteCaCO3strongstrong

AzuriteCu3(CO3)2(OH)2yesstrong

CalciteCaCO3strongstrong

Dolomite(CaMg)(CO3)2weakyes

MagnesiteMgCO3very weakweak

MalachiteCu2CO3(OH)2yesyes

RhodochrositeMnCO3weakyes

SideriteFeCO3very weakweak

SmithsoniteZnCO3weakyes

StrontianiteSrCO3yesyes

WitheriteBaCO3weakweak