Dark Colored Earthy Minerals
PHYSICAL PROPERTIES
MINERAL NAME, FORMULA
 
BRICK RED color; red brown streak; EARTHY LUSTER; H=(variable, but generally soft in the earthy form); heavy.  Looks like rust. HEMATITE, Fe2O3
BLACK, DARK GRAY, DARK GREEN, but light colors are more common; EFFERVESCES (fizzes) IN DILUTE HCl acid; H=3. CALCITE, CaCO3
DARK GRAY, BLACK, but also light colors; commonly in fine-grained granular masses; REACTS WEAKLY WITH HCl acid (slowly or  only if sample is powdered); H=3-3.5. DOLOMITE, CaMg(CO3)2
 


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