Blue calcite from Ihalainen , Finland. Yellow calcite from Crete , Greece. CaCO 3 Crystal system Trigonal. Habitus Calcite is the mineral that shows the most various types of crystals. In my mind is the number of 137 different crystal forms, but I'm not shure about it.
Calcite also occur as fibric aggregates, as coarse to fine grained aggregates or stalactitic.
Cleavage Perfect rhomboedric in three planes, subconchoidal fracture. Hardness 3 Density 2.7 Color usually colorless, but nuances in blue, yellow, green, red, violet, even black and opaque. Streak White to grayish. Luster Vitreous to pearly or dull. Occurance Calcite is the main ingredience of limestone rocks.