1 72 PHYSIOGRAPHY. 



Dolomite. 



eties, provided their faces are not curvilinear or unusually pearly ; also 

 to large grained and easily cleavable varieties, chiefly of greenish colors. 

 Brown-spar comprehends those varieties which possess a reddish brown 

 color. Pearl-spar included crystallized varieties with curved faces, and 

 possessed of a pearly lustre. The massive varieties of granular compo- 

 sition were called Dolomite. 



Before the blow- pipe, some of the varieties assume a darker color, and 

 a higher degree of hardness. They are soluble in acids, but much more 

 slowly than Calcareous Spar, and attended with less effervescence. 



2. It is difficult to judge of the chemical composition of Dolomite. It 

 contains carbonate of lime and carbonate of magnesia ; but the relative 

 quantity of the two has not been accurately settled. From several anal- 

 yses by KLAPROTH, the proportion appears to be nearly as 54*18 ; 

 45-82, which corresponds to 



Lime - 30-55 



Magnesia - - - - 22-18 



Carbonic acid .... 47-26 



Several analyses of brown-spar give very similar results ; others de- 

 viate more or less from them. In general, brown-spar seems to contain 

 more o^-ide of iron and manganese, than either the old varieties dolomite 

 or rhomb-spar. 



3. The different varieties of Dolomite differ in respect to their locali- 

 ties. The granular variety (dolomite) constitutes beds in other rocks, 

 and therefore belongs, itself, to the class of rocks. Rhomb-spar occurs 

 in imbedded crystals and compound masses, in several kinds of rocksj 

 particularly in common Talc, and less frequently in compact varieties of 

 g3J r psum that are mixed with clay. Brown-spar is principally found in 

 metalliferous veins. 



4. The variety called Dolomite occurs in St. Gothard, in the Appen- 

 ines, and in Carinthia ; Rhomb-spar in various districts of Salzburg, the 

 Tyrol and Switzerland, at Miemo in Tuscany, (from which the name of 

 Miemite has been derived,) and in many other countries ; beautiful crys^ 

 tals at Traversella in Piedmont. Brown-spar and Pearl-spar are very 

 frequent at Schemnitz in Hungary, Kapnik in Transylvania, Freiberg 

 ind elsewhere in Saxony, at Clausthal in the Hartz, in Norway arid 

 Sweden, at Alston Moor in Cumberland, in the greywacke quarries of 

 the same country, in Derbyshire, Baeralston and other places in Devon- 

 shire. 



