308 DESCRIPTIVE MINERALOGY. 



This mineral has been ticketed pyroxene, zoisite, and lastly kerolite pseudomorphous of 

 hornblende. The crystalline form, however, is entirely diflferent from either of the two 

 former, and its chemical composition must remove it from the latter. It is most probably a 

 hornblende, altered by an intrusion of alumina and a removal of a part of the silica. The 

 contorted and somewhat fused appearance of many of the crystals clearly point to heat as the 

 agent by which these changes have been produced. The silica which has thus been removed, 

 has combined with the bases of the magnesian limestone, and given rise to other mineral 

 forms. Granular chondrodite and fluor spar are disseminated through the limestone imme- 

 diately associated with this mineral. May not the chondrodite have been formed by the com- 

 bination of the silica which these crystals have lost, and the fluor by the decomposition of 

 the mica ? 



Greyish green mineral. In the same town, and in the same limestone, there are crystals 

 of a greyish green colour, and having the form of long oblique rhombic prisms, with the 

 angles of hornblende. 



The hardness of these crystals scarcely exceeds that of talc. They are sometimes slightly 

 translucent. The powder is white. The following are the results of my analysis of a frag- 

 ment of one of the most perfect crystals, viz : 



SiUca, 34.66 



Alumina, ^ 25.33 



Lime, 5. 09 



Magnesia, 25.22 



Water, 9.09 



In this case, therefore, there is a little less lime and more magnesia than in the preceding ; 

 a difference which is easily explained, as these bodies are isomorphous. The proportion of 

 alumina is also less, but this is made up by the water. 



The nature of the changes which have taken place in this mineral, and the causes which 

 have operated to effect them, are probably similar to those just noticed. 



