148 PHYSIOGRAPHY. 



Quartz. 



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 chief- 

 ly water; and often leaves behind it a mass resembling Opal on desicca- 

 tion, when suddenly exposed to the air. 



5. Common Quartz enters into the regular mixture of various rocks, 

 of granite, gneiss, mica-slate, topaz-rock, &c. In others, they occur in 

 single crystals, and in grains, as, for instance, in porphyry, and are fre- 

 quently met with in vesicular cavities, particularly of amygdaloidal rocks. 

 Here also are found the finest varieties of Calcedony, Carnelian, of the 

 brown, and probably also the red, Egyptian Jasper, the agate balls, &c. 

 Hornstone frequently forms globules in compact limestone ; and Flint, 

 globular and tuberose masses in chalk, often disposed in beds, and inclu- 

 ding petrifactions. Many varieties occur in irregular nodules and large 

 massive concretions, in various rocks. Thus common quartz is found in 

 all those rocks, into whose composition it enters as an ingredient, some- 

 times forming masses, whose interior is lined with crystals. Hornstone 

 and Chrysoprase occur in serpentine rocks, and Fibrous Quartz and 

 Cat's eye in some varieties of slate. Quartz also forms beds by itself, 

 as in quartz-rock and certain kinds of sandstone. It is very frequent in 

 all kinds of veins, where .are found for the most part Amethyst, rock 

 crystals, Hornstone and Calcedony, but chiefly common Quartz, consti- 

 tuting the greater part, and sometimes the whole body of the vein. The 

 agate veins are thus found, which consist of different varieties of Quartz, 

 alternating in various stripes or bands with each other. Rock Crystal, 

 Amethyst, Flinty Slate, but particularly common Quartz, are found in 

 pebbles. The river sand, arid that of deserts, consists of common Quartz. 

 It is also found filling up the space of petrified bodies, as, for instance, 

 echinites in chalk, and petrified wood in sandstone, and in alluvial de- 

 posites. 



6. The numerous varieties of the present species are spread all over 

 the globe, but some of the most distinguished varieties are found only in 

 a few localities. The finest and largest rock crystals are found in the 

 Alps of Salzburg, the Tyrol, Switzerland, Dauphiny, Piedmont, and Sa- 

 voy ;* also in the isle of Madagascar, Ceylon and Brazil. Several vari- 



* About one hundred years ago, a great drusy cavity, lined with crys- 

 tals of this species, was opened in Zinken, which afforded 1000 cwt. of 

 rock crystals, and at that early period sold for $30,000. One crystal 

 weighed eight cwt, others from four to live cwt. 



