THE MINERALOGY OF SCOTLAND. 461 
The absence of magnesia from this sample is peculiar ; as I found that some 
well-defined octahedral crystals from a -vein near Buness House contained 
nearly half as much magnesia as chromium ;—showing chromite to be a true 
spinel. 
2. The substance now noticed was found by me in a single specimen near 
the summit, on the north-west front of the precipitous hill of Haiskeval, in 
Rum. Before analysis I conceived it to be martite. It occurred as a vein of 
about one quarter of an inch in thickness, imbedded in a granular brown belt 
of rock, in augitic trap; this belt was apparently chiefly altered olivine. The 
mineral was granular in structure, jet black in colour, highly lustrous, very hard, 
not magnetic, and had a S. G.=4'163. It was evidently a uniform substance. 
It was first fused with Fresenius’s flux; but, as a small quantity of a fawn- 
coloured powder remained undissolved, a second quantity was fused with 
potassium bisulphate and nitre. No titanic acid being found, the insoluble 
powder of the first fusion was fused with the last-named salts, and found to 
contain chromium. 
It was found that the mineral could not be decomposed by any of the pro- 
cesses usually employed for the ferrous oxide determination; so that the iron 
is merely conjectured to be in the ferrous state. The whole available quantity 
was employed in the analysis. 
The insoluble precipitate of the first analysis was insoluble in hydrochloric 
acid. It was not weighed, but was re-fused, and the ferric oxide and chromium 
sesquioxide separated, and added to the results of the soluble portion of that 
analysis. The quantity of this insoluble precipitate was too minute to give any 
countenance to the view that the total amount of chromium can be assigned to 
an admixture of chromite with magnetite. 
As a large excess was obtained in the first analysis by Fresenius’s flux, 
the mineral was analysed a second time by fusion with potassium bisulphate, 
but with a very similar result. 
The first analysis was by means of Fresenius flux, operating on ‘43 grains ; 
the second by potassium bisulphate, on ‘93 grammes— 
Chromium Sesquioxide, . : : 26 + 304 26° 343 
Alumina, : : , F 17° 957 18-279 
Ferrous Oxide, 5 : ; 5 384: 239 34°112 
Manganous Oxide, . : : : 869 752 
Lime, . : ; ‘ ; : 6°573 6 + 382 
Magnesia, ; ‘ : ‘ 13 * 913 14 - 086 
Silica, . j 4 : ; : 6° 543 6° 236 
106-398 106:191 
Even if the chromium be tabulated as protoxide, there still would be an 
excess of over 2 per cent. 
