PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 29 
longer diagonal of crystals of muscovite. It calls for the exercise of some 
force to separate the plates of the two micas. This is somewhat singular, 
seeing that they are so seldom associated even in the same rock, not to say 
locality. 
Colour very dark brown. Uniaxial, or axial divergence small. 
1°3 grammes yielded— 
Siliea, é , = *43T 
From Alumima, . : ‘03 
‘461 = 35°469 
Alumina, . ; ; . 18°798 
Ferric Oxide, . : . 4°611 
Ferrous Oxide, . : 5 di) Salesyes: 
Manganous Oxide, . 643 
Lime, : ° : *904 
Magnesia, . : - «O07 
Potash; »: , ; IMOSMLSS 
Soda, : ' , : * 238 
Water, : : ; . , 4:97 
100° 016 
Possible impurity, muscovite. 
The “glass” of this mineral was of a dingy green colour, slightly tinged with 
yellow. 
The state of the oxidation and quantity of the iron was twice determined. 
First on ‘4 grammes by hydrochloric acid and fluorspar; secondly, on ° 1407 
grammes by sulphuric acid and fluorspar, yielding identically the same amount. 
From Eajiltration Veins in Granite. 
9. A mass of fine-grained granite occurs on the west shore of Harris, 
opposite to Taransay, forming a point of land which lies intermediate between 
Nishibost and Borve. 
This granite has many veins, plentifully studded with jet black crystals of 
this mica. 
These crystals are here some inches in size, of somewhat unusual hardness, 
and of high lustre. 
They are seemingly of great purity, though occasionally coated with a loose 
ochrey rust. 
They are biaxial to the extent of 2° to 3°. Their gravity is 3°05. 
VOL. XXIX. PART I. H 
