MINERALS
BIOTITE MICA
Composition: Complex hydrous potassium iron magnesium aluminum silicate.
Diagnostic features:
Color: dark green brown, black
Cleavage: one perfect
Large flakes are elastic
Occurrence: same as muscovite
Name: in honor of the French physicist, J. B. Biot.
QUARTZ
Composition: SiO2
Diagnostic features:
Hardness: 7
Luster: glassy
Conchoidal fracture (no cleavage)
(May or may not occur as crystals.)
Occurrence: next to feldspar, the most abundant mineral of the Earth’s crust; found in all three kinds of rocks.
PYRITE
Composition: FeS2
Diagnostic features:
Color: brass yellow (fool’s gold)
Hardness: 6 to 6.5 (hardness of gold is 2.5 to 3)
Streak: greenish-black or brownish-black
Crystal form: cubic crystals are sometimes observed, bearing parallel striations.
Occurrence: found in all three kinds of rocks.
Use: in manufacture of sulfuric acid.
Name: from the Greek word meaning fire, in allusion to the face that when struck with steel it gives off brilliant
sparks.
HORNBLENDE – One of a number of similar minerals collectively referred to as the amphibole group.
Composition: complex hydrous calcium magnesium iron aluminum silicate.
Diagnostic features:
Color: dark green to black
Hardness: 5 to 6
Cleavage: two at angels of 56° and 124°
Crystals: frequently prismatic
Occurrence: in igneous rocks and metamorphic rocks.
Name: from an old German word for any dark prismatic mineral occurring in ores but containing no metal.
CHALCOPYRITE
Composition: CuFeS2
Diagnostic features:
Color: brass yellow, but often tarnished to bronze or iridescent.
Hardness: 3.5 to 4 (less than pyrite).
Streak: greenish-black
Crystal form: usually massive, crystals not observed.
Occurrence: usually found in veins in igneous rocks.
Use: the most widely occurring copper mineral and one of the most important sources of copper.
Name: derived from the Greek word meaning copper and from pyrite.