COMPOUNDS OF CALCIUM. 219 
‘Doiomite.— Calcium-Magnesium Carbonate. Magnesian Carbonate of 
Lime. 
Rhombohedral. & A R=106° 15’. Cleavage perfect pa- 
rallel to R. Faces of rhombohedrons sometimes 
eurved, asin the annexed figure. Often granular 
and massive, constituting extensive beds. 
Color white or tinged with yellow, red, green, 
brown, and sometimes black. Lustre vitreous or 
pearly. Nearly transparent to translucent. Brit- 
mes HW. = 3:34, - GE 2°8-2°9. 
Composition. $CatMg O,C = Calcium carbonate 54:35, 
magnesium carbonate 45°65=100. Some iron or manga- 
nese is often present, replacing part of the magnesium or 
calcium. Dolomite resembles calcite, but differs in that 
unless finely pulverized it effervesces very sparingly, if at 
all, in cold dilute hydrochloric acid. 
The prinepal varieties of this species are as follows : 
Dolomite. White, crystalline granular, often not distin- 
cuishable in external characters from granular limestone. 
Pearl spar. In pearly rhombohedrons with curved faces. 
Rhomb spar, Brown spar. In rhombohedrons, which be- 
come brown on exposure, owing to their containing 5 to 10 
per cent. of oxide of iron or manganese. 
A cobaltiferous variety has a red tint. A white compact 
siliceous variety has been called Gurhofite. Some hydraulic 
limestones are dolomite. 
Diff. Distinctive characters nearly the same as for cal- 
eite. It is harder than that species, and differs in the 
angles of its crystals. and effervesces much less freely; but 
chemical analysis is often required to distinguish them. 
Obs. Massive dolomite is common in Western New Eng- 
land and Southeastern New York, and constitutes much 
of the marble used for building. Crystallized specimens 
are obtained at the Quarantine, Richmond County, N. Y. 
Rhomb spar occurs in tale, at Smithfield, R. I.; Marlboro’, 
Vt.; Middlefield, Mass. ; pearl spar in crystals of the above 
form at Lockport, Niagara Falls, Rochester, Glen’s Falls ; 
gurhofite on Hustis’s farm, Phillipstown, N. Y. 
Dolomite was named in honor of the geologist and tray- 
eler, Dolomieu. 
Dolomite burns to quicklime like calcite, and affords a 
more durable cement. The white massive variety is used 

