146 PHYSIOGRAPHY. 



Quartz. 



There are several massive varieties of common quartz, which consist of 

 granular particles of composition. If they diminish so much in size as to 

 become impalpable, their transparency and lustre becomes diminished, 

 and several kinds of conchoidal fracture appear, if specimens of these va- 

 rieties be broken. This gave rise to new species among the early mine- 

 ralogists. Hornstone is always compound, translucent on the edges, 

 and either of a splintery dull fracture, or glistening and glimmering, and 

 conchoidal. Thus splintery Hornstone and conchoidal Hornstone, are 

 formed, and either of them may produce Woodstone, if it appears in the 

 shape of petrified wood. The varieties of common Flinty slate are most 

 like Hornstone, but show on a large scale, an imperfect slaty fracture, 

 and various dirty grey colors ; those of Lydian stone, which form the 

 second kind of flinty slate, possess an even, glimmering fracture, and 

 a greyish-black color. Flint is a compound mineral, like the two prece- 

 ding ones, but translucent, at least on the edges, and possesses a perfect, 

 flat conchoidal, glimmering fracture. Float-stone, a variety of Quartz, 

 which has likewise been considered as a particular species, consists of a 

 delicate tissue of minute crystals, visible under a powerful magnifier, and 

 demonstrates hornstone and flint, (into which it insensibly passes, by hav- 

 ing its grain closer, and of which it often contains nodules,) to be varie- 

 ties of the same natural-historical species. Common Quartz is some- 

 times found in reniform and stalactitic shapes, consisting of granular par- 

 ticles of composition, sufficiently large to be observed and separated 

 from each other. If the thickness of these individuals be so much di- 

 minished, that at last they become impalpable, the different varieties of 

 Calcedony are formed, occurring in the above mentioned external shapes. 

 The difference in the colors of these, has given occasion to the distinc- 

 tion of common Calcedony, and of Cornelian ; the former of which 

 comprehends greyish colors, or in general such as do not possess bright 

 tints of colors, while the latter refers to red colors. Common Carnelian, 

 moreover, occurs in globular and irregular tuberose shapes ; fibrous 

 Carnelian is found in reniform masses, and generally shows, very dis- 

 tinctly, the above mentioned composition. The rhomboidal crystals, of 

 smalt blue color, from Transylvania, are also enumerated among the va- 

 rieties of common Calcedony ; probably because there exist reniform va- 

 rieties of common Calcedony, possessing the same color, though they are 

 more nearly related to common Quartz. Common Quartz also occurs in 

 massive varieties, showing columnar composition. If they be thin, par- 

 allel, strongly coherent, and more or less bent, Fibrous Qnartz, (a par- 



