COMPOUNDS OF CALCIUM. QE 
-Calcite.—Calc Spar. Calcium Carbonate. 
Rhombohedral. RAM (fig. 1)=105°5’. Cleavage easy, 
parallel with the faces of the fundamental rhombohedron. 

Calcite with the form in fig. 7 is often called dog-tooth 
spar. Occurs fibrous with a silky lustre ; sometimes lamel- 
lar ; often coarse or fine granular, and compact. 
The purest crystals are transparent with a vitreous lustre ; 
the impure massive varieties are often opaque, and without 
lustre, and even earthy. The colors of the crystals are 
either white or some light grayish, reddish or yellowish 
tint, rarely deep red; occasionally topaz-yellow, rose or 
violet. ‘The massive varieties are of various shades from 
white to black, generally dull unless polished. H.=3, 
G.=2°5-2°8. 
Composition. CaO, C=Carbon dioxide 44, ime 56=100. 
Sometimes impure from mixture with iron, silica, clay, 
bitumen, and other substances. B.B. infusible; colors the 
flame reddish, gives up its carbon dioxide, is thereby made 
caustic, in which state it gives an alkaline reaction. Effer- 
vesces in dilute cold hydrochloric acid. Many varieties 
phosphoresce when heated. 
The following are the principal varieties. 
Iceland spar. ‘Transparent crystalline calcite, first 
brought from Iceland. Shows well double refraction. 
Satin spar. <A finely fibrous variety with a satin lustre. 
Receives a handsome polish. Occurs usually in veins tra- 
versing rocks of different kinds. 
Chalk. White and earthy, without lustre, and so soft as 
