234 



Note on the Magnesite. 



[J ULY 



specimens being 2-970, and 2-897, at the temperature of 85°. A good 

 deal of air was given off on its first immersion into water, and it adher- 

 ed to the tongue. 



" Another point to be ascertained, from this mineral, was, whether 

 the circumstance I noticed on the occasion alluded to, would hold true, 

 viz. that calcined magnesia would not become a hydrate, like lime, on 

 slaking, and that this earth might thus be recognized in mixtures. 



" Three of the calcined specimens were treated with water, which 

 disengaged considerable heat, and then exposed in a receiver, over 

 concentrated sulphuric acid, to be ridden of hygrometric moisture. 

 After thirty hours, they weighed respectively 60*45, 58*7, 60*9 grs., 

 shewing an average excess of 10-0, which is about half an atom of 

 water (9-8). This result is so unexpected that it requires further 

 examination, which I hope to be able to give hereafter."* 



With regard to the minerals found associated with the magnesite, we 

 have been favoured by Mr. Fischer, of Salem, with a series of speci- 

 mens, in which chromate of iron and chert are found, both stated by 

 that gentleman to be very abundant in the magnesite formation. 



Mr. Gilchrist of Hoonsoor, informs us that he has discovered a for- 

 mation of magnesite in that neighbourhood, of which a description 

 and specimens are promised us — so that it would seem the localities of 

 this mineral are numerous in southern India. 



M. A. Brongniart thus classifies the magnesite found in Europe, f 



"1. Plastic Magnesite (magnesite plastique), composed of magne- 

 sia, silex and water, without carbonic acid. 



" I here comprise the magnesite so improperly named ecume de 

 Mer, that of the environs of Madrid, that of the environs of Paris, that 

 of Salinelle, department of the Gard, &c. 



Serpentine might, from its composition, almost be referred to this 

 species ; but it is distinguished from it by its Mineralogical charac- 

 ters. 



" 2. Effervescent Magnesite (magnesite effervescente), essentially 

 composed of magnesia and carbonic acid, sometimes associated with 

 very variable proportions of silex and water. 



" We may refer to this division the magnesite of Hroubschitz in 

 Moravia : those of Piedmont, of the isle of Elba, of Baumgarten in 

 Silesia, of Styria, &c." 



* Journal of tie Asiatic Society of Bengal, No. 45, p, 510, 

 t Geological Memoirs, translated by Mr. De la Beche, p. 283. 



