calcite (kalsit)

[L. calx ( calc- ), lime, + -ite2.] Native calcium carbonate, or carbonate of lime, one of the commonest of minerals. It occurs in a great variety of crystalline forms, rhombohedrons, scalenohedrons, etc.; the fundamental form being a rhombohedron with a terminal angle of 105°, parallel to which the crystallized mineral has highly perfect cleav. age, so that a ma of it breaks up with a blow into a great number of small rhombohedrons. The transparent colorle variety is called Iceland spar or doubly refract ing spar, and is used for the prisms of polariscopes. Dog tooth spar is a variety in acute scalenohedral crystals. Satin-spar is a fibrous, and argentine a pearly lamellar variety; the granular, compact, or cryptocrystalline varieties constitute marble, limestone, chalk, etc. Stalactites and stalagmites are forms deposited in limestone caves; calc-sinter, calc-tuff, or or travertin is a porous deposit from springs or rivers which in flowing through limestone rocks have become charged with calcium carbonate. Agaric mineral, or rock-milk, is a soft white variety easily crumbled in the fingers; it is sometimes deposited in caverns. (See cut under