o 



8 ACCOUNT of a MINERAL 



12. The cryflal in its perfcdl condition feems to be a flatted 

 hexagonal prilin, having two broad fides, with two intervening 

 narrow ones, and terminated at either end by a quadrangular 

 pyramid, which, in fome cafes, conftitutes the larger part of the 

 cryftal. When the cryftallization goes on at great leifure, the 

 cryftals are often diftindt and folid. of no iuconflderable magni- 

 tude ; but more commonly with a quicker depofition, they are 

 more flender and delicate and are attached to each other in fuch 

 a manner as to affume a foliaceous form of beautiful appear- 

 ance, refembling fome of the fern tribe in their pinnated frons, 

 to fpeak botanicHJly ; but in this arrangement, a confiderable 

 diverfity occafionally happens. 



13. The cryftals obtained from calcined barytic fpar, in the 

 manner now defcribed, dilfolve in water, and impart the qua- 

 lities of barytic water ; they change vegetable colours to a 

 green, they unite with acids without effervefcence, and gene- 

 rate with the muriatic and fulphuric, compounds fimilar to the 

 fulphate and muriate of barytes ; hence 1 infer they confift of 

 pure barytes. 



14. These cryftals are perfedly tranfparent and colourlefs, 

 but when expofed to the air, become white, opaque and efFer- 

 vefcent, lofing during this change nearly 30 pe?- cent, of their 

 weight. Subjeded to the heat of boiling water, they undergo 

 the aqueous fufion and become fluid ; from which ftate, if al- 

 lowed to cool flowly, they concrete into a folid cryftalline mafs. 

 When a ftronger heat is applied, and continued till all the moi- 

 fture is difljpated, there remains a white powder, lighter by 

 one half than the cryftals employed, which, urged by the 

 heat produced by the blowpipe, is melted with more difficulty 

 than the native carbonate. 



15. The folubility of thefe cryftals in water furprifed me a 

 good deal. One ounce of dirtilled watrr, at temperature 60, 

 diffolves almoft twenty-five grains, while boihng water appears to 



I be 



