TIREY. MINERALS. ,55 



Their summits are sometimes truncated, but no further 

 regular modifications of this part of the crystal were 

 observed. 



A regular transition occurs between the sahlite thus 

 described and coccolite, exactly similar to that which 

 takes place in the augit; and masses of coccolite are 

 thus found of considerable size and of different co- 

 lours. The most remarkable of these is snow white and 

 opake, forming a new and beautiful variety of this sub- 

 stance. From this it passes into various shades of grey, 

 equally loose in texture, and falling into distinct grains 

 when injured. The specific gravities of these several 

 varieties are nearly the same ; and it is remarkable that 

 the whitest varieties which seem to contain no metallic 

 matter, are equal in weight to the darkest, which con- 

 tain so large a proportion of iron. 



The sahlite, as I have already mentioned, is frequently 

 accompanied by tremolite. The crystals of both sub- 

 stances are often intermingled and confounded together, 

 or a crystal of the former penetrates and mixes with on& 

 of the latter in so intimate a manner, that as the two sub- 

 stances have frequently the same colour and splendour, it 

 is not easy to distinguish them. In one of the spe- 

 cimens found, a crystal is divided longitudinally, the 

 one half being of tremolite the other of sahlite. The 

 tremolite presents a very beautiful variety; forming 

 groups of separate crystals, which are in the usual shape 

 of very flat rhomboidal prisms, interwoven together in a 

 distinct manner and with large cavities interposed; the 

 crystals being two inches in length and three quarters of 

 an inch in breadth. In texture it is glassy, and being 

 translucent or nearly transparent, is of a watery white* 

 Mica is found intermixed with the sahlite, in small crystals 

 of a talcose aspect; and it occurs in a similar state in 

 the limestone of Glen Elg, accompanying the two mi- 

 nerals above mentioned. 



The last mineral to be noticed is sphene, which is 



