328 PHYSIOGRAPHY, CLASS II. 



able, Iron-Flint is produced, 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, no longer be recognized. 

 Striped 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 form- 

 ed 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 jasper of uncleavable Quartz, and 

 does not belong to the present species, nor does Porcelain- 

 Jasper, which is nothing else but burnt clay. 



3. The most perfect varieties of rhombohedral Quartz 

 are pure Silica, Si, which contains 49-70 silicium and 50-30 

 oxygen. BUCHOLZ obtained 09.375 of silica from Rock- 

 crystal, with traces of iron and alumina. Hornstone, 

 Flint, and Calcedony agree with it, according to various 

 analyses of the ablest chemists. Several varieties contain 

 small quantities of alumina, lime, oxide of iron, &c. 

 Chrysoprase contains 0-01 of oxide of nickel, according to 

 KLAPROTH. Rhombohedral Quartz is infusible before the 

 blowpipe, and shews itself to be pure silica. It is dissolv- 

 ed by soda easily and with effervescence. According to 

 VAUQUELIN, it colours an infusion of violets green, if re- 

 duced to powder. Two pieces rubbed together emit an 

 empyreumalic odour, and a phosphorescent light. Crystals 

 of rhombohedral Quartz may be obtained as deposits from 

 a solution of silica in fluoric acid, or in potash diluted with 

 water. The fluid from which crystals of this species are 

 formed in geodes and other natural cavities of rocks, has 

 been observed to be chiefly water, and often leaving be- 

 hind it a mass resembling opal on desiccation, when sud- 

 denly exposed to the air. 



4. The varieties of rhombohedral Quartz are of the 



