42, ELEMENTARY GEOLOGY 
carry in solution many salts which have been formed 
by the decay of feldspar. 
The Calcite Group. — Calcite (Figs. 4 and 6), car- 
bonate of lime (CaCQ,), though commonly white, may 
be of any color. It crystallizes in various forms (such 
Fig. 6. 
A group of calcite crystals. 
as rhombs, dog-tooth crystals, etc.), but although usually 
crystalline, it is frequently amorphous. The mineral 
is so soft that the knife easily scratches it. It is 
hght in weight, and, when it breaks, cleaves (Fig. 4) 
readily in two or three directions. Indeed, in the 
crystals of calcite, the cleavage planes may be seen 
cutting the mineral into rhombic blocks. 
