504 RUM. MINERALS. 



the latter forming concretions of an inch or more in 

 length. It is by no means abundant in this place. 



This hypersthene is accompanied by a mineral, also 

 rare, and hitherto unobserved in Scotland ; namely, apa- 

 tite. The crystals are very minute, not exceeding half 

 an inch in length and as slender as a pin, but perfectly 

 characterized. The position of this mineral is analogous 

 to that which it sometimes occupies in volcanic rocks, 

 in which however it is by no meajis common, having 

 hitherto occurred chiefly in the primary rocks, in granite, 

 gneiss, and micaceous schist. 



I may add, that dark felspar, similar to that of Labrador, 

 and brown mica, are occasionally found in the same vein. 



In the heliotrope, cavities of a large size are sometimes 

 found, filled with an opake green calcareous spar; pre- 

 senting a very uncommon variety of that substance, and, 

 like the chalcedony, apparently coloured by the green 

 earth. 



The last mineral which remains to be enumerated, being 

 hitherto undescribed, it is necessary to enter into a minuter 

 detail respecting it. Many years have passed since I 

 discovered it, both here and in Fife ; and the description 

 has been hitherto delayed in hopes of finding larger spe- 

 cimens, better adapted for elucidating its history. These 

 hopes have hitherto been disappointed, and I must there- 

 fore give it, however imperfect; in hopes that other 

 mineralogists will hereafter supply the deficiencies. When 

 recently broken it is of a green colour; varying from 

 the transparent yellow green of the finest olivin, (or 

 chrysolite) which it sometimes resembles so as to be 

 undistinguishable, to the dull muddy green of steatite, 

 to which in this case it bears an equal resemblance. In 

 a few hours after being taken from its repository, or 

 exposed to the air, it turns darker and shortly becomes 

 black ; a change which also occurs within the rock at 

 the depth of an inch or more from the surface. In this 



