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MINERAL NAME, FORMULA | |
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BLACK to DARK BROWN; PERFECT 1-WAY CLEAVAGE; thin flexible sheets; flakes in small grains; H=2.5. | BIOTITE,
K(Fe,Mg)3AlSi3O10(OH)2 |
| GREEN to GREENISH BLACK color; scaly; 1-way cleavage; H=2. | CHLORITE,
(Mg,Fe)6Si4O10(OH)8 |
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| BLACK, DARK GRAY, DARK GREEN, but light colors are more common; 3-WAY CLEAVAGE, not at right angles; EFFERVESCES (fizzes) IN DILUTE HCl acid; H=3. | CALCITE,
CaCO3 |
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| DARK GRAY, BLACK, but also light colors; 3-WAY CLEAVAGE, not at right angles; commonly in fine-grained granular masses; REACTS WEAKLY WITH HCl acid (slowly or only if sample is powdered); H=3-3.5; may occur as curved, pink crystals. | DOLOMITE,
CaMg(CO3)2 |
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