THE MINERALOGY OF SCOTLAND. 



349 



axis of dimorphous substances lying parallel to one another, as known to occur with 

 grenatite and kyanite, and with other di-morphs. 



In this third form it is somewhat more brittle than in the others, but it is still 

 reduced to powder with extreme difficulty. I with difficulty separated a sufficiency of 

 the fibrolite in its third form for analysis ; but when separated it was exquisitely pure 

 and brilliant. It had a hardness fully 7' in the scale. 



22 "1 grains yielded — 



Silica, 

 Alumina, . 

 Ferric Oxide, . 



Manganous Oxide, 

 Water, 



38'410 

 61-426 

 •215 

 •114 

 •23 



100-395 



3. Fibrolite from Pressendye Hill, Tarland, Aberdeenshire. 



The specimens examined I found in small quantity coating gneiss, in thin veins on 

 the north-west side of the hill, at about 300 yards from its summit. 



Its colour was dull white ; it was not very lustrous ; it was in fibrous and slightly 

 matted tufts, which were very tough. No piece was got large enough for the determina- 

 tion of the specific gravity. 



It yielded — 



39-680 



kJ-L-UAJOi, ..... 



Alumina, ..... 



. 58-822 



Ferrous Oxide, 



•038 



Manganous Oxide, . 



1-100 



Potash, 



•860 



Soda, 



trace 



Water, 



•320 



100-820 



Dr Thomas Aitken of Inverness showed me fragments of granite boulders which he 

 had collected at Auchendown, near Cawdor. These contain a substance of an appear- 

 ance very similar to the last. There is, however, some suspicion in my mind that this 

 may be merely somewhat plicated plates of a hydrous mica, which show the edges of 

 the plates only. The specimens, having been exposed, are not altogether fresh. 



There is one fact which so far increases the probability of this being fibrolite, namely, 

 that a black mica, which has much the appearance of that associated with the mineral 

 it Clashnaree, is present in the Auchendown boulders. 



Kyanite, A3 Si. Anorthic. 

 There is good reason to believe that this species was first found in Scotland, 



VOL. XXXIX. PART II. (NO. 11). 3 G 



