PHYSIOGRAPHY. 171 



Dolomite. 



Compound Varieties. Twin-crystals. 



Fig. 162. 



Piedmont. 



Sometimes variously repeated. Implanted globules; bo- 

 tryoidal, fructicose, and other imitative shapes : surface 

 drusy and rough, composition columnar. Massive : com- 

 position granular, of various sizes of individuals, generally 

 easily distinguishable, and often but slightly cohering. The 

 composition is often columnar, also of different sizes of in- 

 dividuals. These compositions are again variously com- 

 pounded, as the granular composition in a coarser kind of 

 granular composition, of which the component particles may 

 be easily separated, and present an uneven surface. It oc- 

 curs often in crystalline coatings upon other crystals, im- 

 pressions, &tc. 



1. The remark which was made under Calcareous Spar, respecting its 

 comprehension of several distinct species, separated from one another by 

 constant differences of form, hardness and specific gravity, may be appli- 

 ed to Dolomite with nearly the same propriety. Arid the mineralogist 

 there referred to, who has attempted to distinguish those species, has oc- 

 cupied himself also with the varieties of the present species. Some ac- 

 count of his labors will be introduced as an appendix to Dolomite. 



The division of this species into sub-varieties and sub-species, accord- 

 ing to the older mineralogists, depended upon slight variations of compo- 

 sition, color, lustre, and upon chemical and mechanical mixtures. 

 Rhomb-spar and Bitter-spar are the names applied to crystallized vari- 



