214 OF A VARIETY OF THE CORUNDUM. 



the natural ftate in which they exift, as ingredients of com- 

 plex ftones, we rauft confider the refult of chemical analyfis, 

 but as an approximation towards the ftriclnefs of truth. 



As the intrufion of the oxide of titanium into the place, 

 , . which has been ufually occupied by the oxide of iron, confti- 

 tutes this ftone a variety of the adamantine genus, I have been 

 induced to record my experiments. I am aware, however, 

 that it may be juftly obferved, that the oxide of neither metals 

 is effential to the nature of the corundum. 

 Oxide of tita- I have no doubt, but that the oxide of titanium will be found 



mum often met to \^ G more plentifully fcattered abroad throughout the mineral 

 kingdom, than it has been hitherto imagined. I have detected 

 it in a fpecies of fhirl, which occurs in a large cryfiallized 

 mafs, on the tenement of Botallack, in the parifh of Juft, in 

 this county. It compofes feveral alternate beds or floors of 

 varying dimenfions. — The compaclnefs of thefe beds not hav- 

 ing allowed the cryftals to (hoot with freedom in any direc- 

 tion ; It is rarely that they occur with their terminations com-' 

 pleat. — Thefe, however, in no refpect differ from the common 

 form, and vary only in the length of the prifm, from £ of an 

 inch to an inch. — The colour of this fhirl is black. — I have 

 alfo lately difcovered the oxide of titanium in two fpecies of 

 bafalt, of the form of large pebbles, which I found near the 

 fea-fhore. Whether they are natives, or whether they were 

 dropped upon our coaft accidentally as ballad: from fome vefTel, 

 I have not as yet had an opportunity of afcertaining. That 

 they are real bafults, I reft upon the authority of one on whom 

 I can fafely rely, whofe^nowledge in mineralogy can be only 

 equalled by his friendly difpofition to communicate it. I 

 mean John Hawkins, Efq. 



My experiments alfo proved, that they contained all the 

 known ingredients of bafalts, with the addition of the oxide 

 of titanium. 



Creed, near Grampound, Cornwall, 

 March 2, 1 803. 



letter 



