PHYSIOGRAPHY. 147 



Quartz. 



ticular species of the old systems,) is formed ; Cat' s eye, (another spe- 

 cies,) if they are nearly impalpable, and almost solely to be observed ia 

 the opalescent light, which they exhibit when cut into a convex sur- 

 face. Cat's eye is generally greenish grey ; but there are varieties of 

 other shades, sometimes even black. It preserves a small conchoidal 

 fracture, and is more or less translucent. If several of the preceding va- 

 rieties are distinctly colored by some foreign mineral substance, or inti- 

 mately mixed with it, various other pretended species are formed. 

 Chrysoprase is a variety of common Quartz, consisting of small granu- 

 lar particles of composition, colored apple green by oxide of nickel ; 

 Plasma is a variety of Calcedony, colored leek-green, and almost grass 

 green, by some substance which is not exactly ascertained. Heliotrope, 

 likewise a variety of Calcedony, but mixed and colored by green earth, 

 containing blood-red spots of Jasper. The brownish-red color of the 

 commonly so called Hyacinth of Compost ell a, is produced by the admix- 

 ture of oxide of iron. If the same thing takes place in compound varie- 

 ties, the individuals of which are still recognizable, Iron Flint is produ- 

 ced ; and Jasper, with its various kinds, is formed, if besides the oxide 

 of iron, clay enters into the mixture ; and if, moreover, the individuals 

 can, on account of their diminutive size, be no longer recognized. Stri- 

 ped Jasper probably contains a good deal of clay, and is distinguished on 

 account of its striped delineations. The varieties of Egyptian Jasper, 

 both Red and Brown, occur in globular shapes ; the latter of which are, 

 beyond a doubt, formed in open spaces, as appears from the concentric 

 layers of which they consist, and the drusy cavities lined with crystals of 

 Quartz, often found in their interior. Agate Jasper, being less impure, 

 is more properly referred to Hornstone. Opal Jasper may be said to be 

 a variety of Opal, and does not belong to the present species ; nor does 

 Porcelain Jasper, which is nothing else but burnt clay. 



3. Quartz is infusible before the blow-pipe, on charcoal, but with soda 

 it is easily dissolved, with effervescence. 



4. Analysis. 



The most perfect varieties of Quartz, consist of pure silica. Bu- 

 CHOLZ obtained 99*375 of silica from Rock crystal, with traces of iron 

 and alumina. Hornstone, Flint and Calcedony, agree with it according 

 to various analyses. Several varieties contain small quantities of alu- 

 mina, lime, oxide of iron, &c. Chrysoprase contains 0-01 of oxide of 

 Nickel, according to KL.APROTH. Crystals of Quartz may be obtained 

 as deposits from a solution of silica in fluoric acid, or in potash diluted 



