364 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



having established its being a constituent part of the sapphire, the small proportion 

 of -£*., cannot be expected to produce a very notable difference. It is not neces- 

 sary to do more than thus to hint at what further analysis and examination of for- 

 mer experiments are required, to ascertain the analogy or identity of the sapphire 

 and oriental ruby with corundum. 



I have before stated, that I have corundum (which has the same texture and 

 fracture as the common colourless corundum) of a ruby red, and also of sapphire 

 blue, and of sapphire blue and white colours. I have sapphires, yellow and blue, 

 white and blue, brown and greenish, and of a purplish hue ; these I should con- 

 sider as corundum, with fracture of vitreous lustre. Mr. Tranckell, who resides in 

 Ceylon, and from whose communications I derived lately much information, had, 

 about 5 years ago, a sapphire, the greater part blue, and the remainder of a pale 

 ruby colour. I saw, in Rome* de l'lsle's collection, at Paris, a small gem, which 

 was yellow, blue, and red, in distinct spots, and he called it oriental ruby. M. de 

 la Metherie, to avoid the confusion of the denomination oriental ruby with octoe- 

 dral ruby, calls it a sapphire ; with more correctness, I think, the above-mentioned 

 gems should be classed as argillaceous, under the denomination of corundum. 



I am not uninformed that corundum is said to be found in France. The Count 

 de Bourbon is convinced, that the specimens mentioned in Crell's Journal, as 

 having been found by him in a granite in the Forez, were corundum. M. Morveau 

 also says, he found it in Bretagne ; but the Abbe Hauy, in the Journal de Mines, 

 N° 28, asserts, that the corundum found in France is titanite : he does not say 

 whether this observation extends both to the corundum of Bretagne and that of the 

 Forez. In the same manner I had observed, in the specimens which Mr. Raspe 

 called jade, or a new substance, from Tiree, on the west coast of Scotland, a great 

 resemblance to corundum ; but having then only had a cursory view of the sub- 

 stance, I am indebted to Mr. Hatchett for the examination of a specimen of it 

 which he had from Mr. Raspe's collection. 



The Tiree stone resembles crystallized corundum of the coast, in texture and 

 colour ; it is also as refractory, when examined by the blow-pipe, with different fluxes. 

 Its specific gravity is 3.049; consequently nearer the specific gravity of pure co- 

 rundum than the above-mentioned lump, 2.785, and the matrix of corundum, 

 2.768. The Tiree stone will scratch glass readily, ,but not rock crystal ; its hard- 

 ness therefore corresponds with that of the matrix of corundum. The substance of the 

 lump before described in page 35Q, cuts glass, and rock crystal, and theTiree stone, 

 readily. It will therefore be sufficient for me to say, that there is great probability 

 corundum may be found in Great Britain, and on the continent of Europe, as well 

 as in Asia ; and the above slight assays may show, that observations on corundum, 

 in its different states of purity, may lead to accurate distinction between substances 

 hitherto imperfectly known, and will lead to a revision of the siliceous genus, by 

 which the argillaceous genus may obtain its due pre-eminence in mineralogy. 



When gems, by art, or by rolling in the beds of rivers, have been deprived of 



