Minerals - Short Notes

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.