DOLOMITE. 113 
century, it was demonstrated that the rock Dolomite had a 
similar composition to the crystallized forms of the mineral, 
and the name Dolomite is now applied to both varieties. 
Both calcic carbonate and magnesic carbonate occur in 
the massive and the crystalline form: the former as calcite 
when crystalline and as limestone when massive: the latter 
as breunnerite when crystalline and as magnesite when 
massive. These two minerals, being very nearly isomorphous, 
can replace each other in any proportions without affecting 
the appearance of the minerals, beyond causing some minute 
difference in the angles of the crystals. The massive 
variety of any of these minerals seldom occurs free from the 
other. The term Dolomite is restricted to minerals con- 
sisting of carbonate of lime and carbonate of magnesia in 
approximately equal atomic proportions, so that its typical 
formula would be CaCO3 + MgCO3. But as a series of 
minerals can be obtained varying from this to a calcite 
containing but a trace of magnesia, or to a magnesite con- 
taining but a trace of lime, the term Dolomite must be 
closely restricted to minerals of the above formula. It is 
not an accidental member of such a series, it is a definite 
species, and possesses individual chemical and_ physical 
properties. 
The evidence for assuming that Dolomite is a true 
mineral and not an accidental mixture of calcite and mag- 
nesite is adduced from the following. When dolomite and 
calcite occur, as they at times do, co-mingled in the same 
rock, so that the mass upon analysis might be put down 
merely as magnesian limestone, the dolomite and calcite 
can nevertheless be separated by the action of dilute acid, 
which dissolves the calcite, leaving dolomite and not mag- 
nesite, as would be the case if dolomite itself were but a 
mixture of calcite and magnesite. Dr. T. Sterry Hunt 
found that dilute acetic acid containing 15% of glacial acid 
and kept at o°C will not attack dolomite, or only with 
