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PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
The white orthoclase of these veins is plentifully studded with crystalline 
masses of magnetite, and intersected by large plates of a dark brown-black 
mica, which are disposed more or less parallel to the sides of the vein, so as to 
exhibit only their edges on its glaciated section. 
These edges are frequently eight to ten inches in length; some, measured 
by my confrere Mr Dupcron and myself, were fifteen and sixteen. This mica 
splits readily into plates of considerable size, being tough, and not brittle like 
those of lepidomelane. 
The plates transmit light of a dark brown-black colour, and are slightly 
biaxial. The mineral is powdered with extreme difficulty ; the powder is black, 
with a slight shade of green. 
The specific gravity is 3 ° 03. 
1°34 grammes gave— 
Silica, 3 , -486 
From Alumina, : *012 
A498 = Bre 64 
Alumina, . : : . 15°006 
Ferric Oxide, : : ee ots) 
Ferrous Oxide, . f Sey “Ooo 
Manganous Oxide, : . 1:044 
Lime, 1°128 
Magnesia, ; 1 88188 
Potash, : : : me eras 
Soda, 1°605 
Water, 221 
100-16 
The specimen seemed absolutely pure. The glass was of a light olive 
brown colour over the Bunsen; of a light blue after having been subjected 
to the heat of the blast furnace. 
The state of the oxidation of the iron and its quantity were twice deter- 
mined,—on both occasions by the action of calcium fluoride * and sulphuric 
acid,—a stream of carbonic acid being passed, during the whole process, through 
the apparatus. 
On the first occasion :1178 grammes yielded of ferrous oxide, 17 : 26 
per cent.; on the second -172 grammes yielded of ferrous oxide, 17° 443 
per cent. 
* My assistant, Mr Dauzrnt, finds it advisable to use a mixture of potassium fluoride and calcium 
fluoride—the former being in excess. Less calcium sulphate is thus formed, and the platinum crucible 
is more speedily emptied of its contents. 
