Mineral identification

Magnetite

• Magnetic 

• Black or dark grey 

• Black streak 

• Harder than a glass plate

Pyrite/Pyrrhotite

• Non magnetic 

• Gold, brassy yellow 

• Black streak 

• Harder than a penny

  

Galena

• Nonmagnetic 

• Silvery or battleship grey 

• Grey streak 

• Softer than glass, harder than a penny 

• Three cleavage directions at 90º

Heratite

• Nonmagnetic 

• Silvery or battleship grey 

• Reddish Brown streak 

• Softer than glass, harder than a penny 

• Breakage may occur in smooth mounds

Graphite

• Nonmagnetic 

• Silvery or battleship gray 

• gray-black streak 

• Softer than a fingernail 

Biotite

• Splits into thin sheets

• Softer than a penny

• Dark brown, black, greenish gray or brown, green 

• Elastic cleavage sheets, transparent  

Chlorite

• Splits into thin sheets 

• Softer than a penny 

• Dark brown, black, greenish gray or brown, green

• Flexible cleavage sheet; opaque

Pyroxene family

• About the hardness as glass

• Cleave in two different directions at 87º and 93º

• Darkish green or brown 

• Commonly in elongate crystals 

Amphibole

• About the same hardness as glass 

• Cleavage in two directions at 56 and 124º

• Dark green or brown 

• Commonly elongate or needlelike crystals

Plagioclase feldspar 

• Striations on one cleavage direction; may be iridescent 

• white , gray, black 

• Cleavage in two directions at 90º

• Harder than glass

Potassic feldspar

• No striations; may have narrow, ribbonlike exsolution lamellae 

• White, gray, pink, green

• Cleavage in two directions at 90º

• Harder than glass

staurolite

• Often in stubby crystals; may occur as cross-shaped pairs of crystals 

• brown , reddish brown 

• Cleave in two directions not at 90º

• Harder than glass 

Quartz

• Often in elongate six-sided crystals 

• Variable in colors

• Conchoidal fracture 

• Harder than glass

Garnet

• Often in equant 12-sided crystals 

• Red, green

• Conchoidal fracture

• Harder than glass

Olivine

• May occur in granular masses 

• Green

• Conchoidal fracture 

• Harder than glass

Muscovite

• Softer than a fingernails 

• Prominent cleavage in one direction 

• Colourless 

• Splits into thin transparent sheets

Talc

• Feels greasy 

• White, gray 

• Prominent cleavage in one direction 

• Softer than a fingernail 

Gypsum

• Splits into slabs; massive variety is fine grained, granular 

• White, colorless 

• Prominent cleavage in one direction 

• Soften than fingernail 

Calcite

• Reacts vigorously with hydrochloric acid

•  colorless , gray, white, pink 

• Cleavage in three directions not at 90º

• Harder than a penny, softer than glass

Fluorite

• Cube-shaped crystals 

• Colorless, purple, green 

• Cleavage in four directions

• Harder than a penny, softer than glass

Kyanite

• Flat, bladed crystals; H=5.5 parallel to long side, H= 7 parallel to short side 

• Blue, gray 

• Cleavage in two directions not at 90º

• Harder than glass

Corundum

• H=9; commonly in six-sided prismatic crystals with flat breakage planes at end 

• Gray, brown (gern varieties red, blue) 

• No breakage (may show smooth flat breakage)

• Harder than glass