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COMMON ROCK-FORMING MINERALS

Mineral Definition: naturally-occurring, inorganic solid with an ordered atomic arrangement and well-defined chemical composition

Metallic Luster

GALENA: silver color, gray streak, 3 cleavages at 90°

PYRITE: gold color, gray streak, cubic crystals, no cleavage

Nonmetallic Luster
Dark Color		Light Color
Harder Than Glass	OLIVINE: green, no cleavage, glassy luster	Harder Than Glass	QUARTZ: variable color, no cleavage, fracture
	PYROXENE: green or black, 2 cleavages at 90°		PLAGIOCLASE: white to gray-blue, 2 cleavages at 90° , striations (*2 types)
	AMPHIBOLE:green or black, 2 cleavages not at 90°		K-FELDSPAR: white to pink, 2 cleavages at 90° , no striations
Softer Than Glass	BIOTITE: black, 1 perfect cleavage (produces sheets)	Softer Than Glass	MUSCOVITE: clear to translucent, 1 perfect cleavage (produces sheets)
	HEMATITE: red or red-brown, no cleavage, dense		HALITE: clear to white, 3 cleavages at 90° (salt)
	LIMONITE: yellow or yellow-brown, no cleavage		CALCITE: clear to white, 3 cleavages not at 90° , reacts to weak acid
			FLUORITE: variable color, 4 directions of cleavage not at 90° (often produces odd-shaped fragments)

GALENA

Chemical Formula: PbS (lead sulfide) Mineral Group: sulfides Luster/Color: metallic/silver-gray Cleavage: 3-directions at 90^o Hardness: 2.5 Other Characteristics: high specific gravity (7.6), gray streak, mined for lead (lead ore)

PYRITE

Chemical Formula: FeS₂ (iron sulfide) Mineral Group: sulfides Luster/Color: metallic/gold or brassy-yellow Cleavage: absent Hardness: 6 to 6.5 Other Characteristics: common cubic crystals, high specific gravity (5)

HEMATITE

Chemical Formula: Fe₂O₃ (iron oxide) Mineral Group: oxides Luster/Color: non-metallic (sometimes metallic)/red-brown Cleavage: absent Hardness: 6.0 Other Characteristics: red-brown streak, high specific gravity (5), commonly associated with limonite, granular or massive aggregates

LIMONITE

Chemical Formula: Fe₂O₃^.H₂O (hydrated iron oxide) Mineral Group: oxides Luster/Color: non-metallic/yellow brown Cleavage: absent Hardness: 5 to 5.5 Other Characteristics: yellow-brown streak, moderate to high sepcific gravity (3.5-4), commonly associated with hematite, massive or fibrous aggregates

CALCITE

Chemical Formula: CaCO₃ (calcium carbonate) Mineral Group: carbonate Luster/Color: non-metallic, often glassy/usually colorless or white, otherwise variable Cleavage: 3 directions at 75^o and 105^o Hardness: 3 Other Characteristics: reacts to weak HCL acid

HALITE

Chemical Formula: NaCl (sodium chloride) Mineral Group: halides Luster/Color: non-metallic/mostly colorless Cleavage: 3 directions at 90^o Hardness: 2 to 2.5 Other Characteristics: salty taste, high solubility

FLUORITE

Chemical Formula: CaF₂ (calcium fluoride) Mineral Group: halides Luster/Color: non-metallic, often glassy/variable Cleavage: 4 directions Hardness: 4 Other Characteristics: cubic crystals, dipyramidal cleavage fragments

MUSCOVITE

Chemical Formula:KAl₂(AlSi₃)O₁₀(OH)₂ Mineral Group: non-ferromangnesian silicate Luster/Color: non-metallic, glassy/colorless Cleavage: 1 perfect direction Hardness: 2 to 3 Other Characteristics: splits into thin elastic sheets, transparent to translucent

BIOTITE

Chemical Formula: K(Mg,Fe)₃(Al,Fe)Si₃O₁₀(OH)₂ Mineral Group: ferromagnesian silicate Luster/Color: non-metallic, glassy/black Cleavage: 1 perfect direction Hardness: 2 to 3 Other Characteristics: splits into thin elastic sheets, opaque to barely translucent

OLIVINE

Chemical Formula: (Fe,Mg)₂SiO₄ Mineral Group: ferromagnesian silicate Luster/Color: green Cleavage: absent Hardness: 6.5 to 7 Other Characteristics: transparent to translucent, commonly occurs as small granular aggregates

PYROXENE

Chemical Formula: complex solid solution Mineral Group: ferromagnesian silicate Luster/Color: non-metallic/green to black Cleavage: 2 directions at 90^o Hardness: 6 Other Characteristics: breaks into columnar fragments

AMPHIBOLE

Chemical Formula: complex solid solution Mineral Group: ferromagnesian silicate Luster/Color: non-metallic/ green to black Cleavage: 2 directions at 56^o and 124^o Hardness: 6 Other Characteristics: breaks into wedge-shaped splintery fragments

QUARTZ

Chemical Formula: SiO₂ Mineral Group: non-ferromagnesian silicates Luster/Color: non-metallic, glassy/variable Cleavage: absent Hardness: 7 Other Characteristics: conchoidal fracture, high hardness

CALCIUM-PLAGIOCLASE

Chemical Formula: CaAl₂Si₂O₈ Mineral Group: non-ferromagnesian silicates Luster/Color: non-metallic, glassy/blue-gray Cleavage: 2 directions at 90^o Hardness: 6 to 6.5 Other Characteristics: striations, gray color with iridescence (play of colors)

SODIUM-PLAGIOCLASE

Chemical Formula: NaAlSi₃O₈ Mineral Group: non-ferromagnesian silicate Luster/Color: non-metallic, glassy/ white to light gray Cleavage: 2 directions at 90^o Hardness: 6 to 6.5 Other Characteristics: striations, light color

POTASSIUM-FELDSPAR

Chemical Formula: KAlSi₃O₈ Mineral Group: non-ferromagnesian silicate Luster/Color: non-metallic, glassy/pink to white Cleavage: 2 directions at 90^o Hardness: 6 to 6.5 Other Characteristics: absence of striations