THE MINERALOGY OF SCOTLAND. 435 
blue colour. I have ascertained that this they sometimes are, to the extent at 
least of containing manganese. The substance I now notice is one such. 
It occurs as a thin coating on red granite, in the upper quarry of Craigton, 
Hill of Fare, Aberdeen. Colour blue-black, here and there with the lustre of 
graphite; cuts with knife. Being only a thin coating, it was dissolved off the 
granite with very weak hydrochloric acid, which seemed hardly to affect the 
lepidomelane present in the granite ; which seemed to be otherwise altogether 
unaffected. It contained, in addition to the lepidomelane, only red orthoclase 
and quartz. 
Analysis of the solution gave— 
Alumina, . ’ ; : p : 32°203 
Ferric Oxide, d : ; ; : 38°305 
Manganous Oxide, c é 7°458 
Magnesia, . . ; : 5 16°61 
Potash, ; : ; ; , 3 4°'745 
Soda, . : ‘ ’ : : ; ‘678 
Silica, . ; : ‘ ; . f trace. 
Chlorine was evolved during the solution, so that the manganese must have 
been partly at least in the state of Mn,O,. 
This is the only specimen of such dendritic coatings which I have got in 
quantity sufficient for analysis, But the result lends some countenance to our 
considering such coatings, especially when they occur in Old Red Sandstone, as 
being, like this, a very impure wad. I have attached the name, merely to 
draw attention to this substance. 
NATIVE TRON. 
A chromiferous magnetite, afterwards to be noticed as occurring in the bed 
of the Dale Burn in Unst, was found to be so difficult of decomposition that 
comminution under water, with repeated decantation, was had recourse to. 
Towards the conclusion of the process, the pestle was found to jump over a 
number of particles which no force could reduce to powder, though several 
were found to be flattened out by the pressure into thin scales. These were 
thoroughly washed, and found to be strongly magnetic. When placed in an 
acidified solution of a copper-salt, they became instantly coated with the red 
metal. They readily dissolved in acid without residue, and gave the tests for 
iron. In the pounding of the magnetite it had never been touched by an iron 
or steel tool; and, from the time when they were collected to that in which 
they were examined as above by him, they were never out of the writer's 
possession. ‘These grains, therefore, are nutive tron. 
VOL. XXX. PART IL, 3 Y¥ 
