426 NATURAL HISTORY. 



making various articles, as boxes, handles for doors or 

 locks, etc. 



Jasper is a compact, nearly or quite opaque, silicious 

 rock of a dull red or yellow color, caused by its contain- 

 ing some clay and yellow or red oxyd of iron ; some 

 varieties are of green and other shades. It mostly 

 occurs in the form of globular stones which, on being 

 cut or sawed through, exhibit innumerable delineations 

 of color and shapes. There are many species of jasper, 

 all of which are useful, some being employed in paving, 

 others are made into grind-stones, and the black, also 

 called Lydian Stone, 



Basanite or Touch Stone is used for trying the 

 purity of the precious metals. Found in clay strata in 

 the Black Forest, Hartz, Saxony, and Silesia. Admits 

 of a high polish, but is never used as a gem. 



Agate is a composite stone made up of chalcedony, 

 jasper, hornstone, and amethyst. It is of spherical 

 form, and occurs mostly among clay-porphyry. Agate 

 stones are frequently hollow and contain crystals in the 

 cavities. Native in the elevated mountain formations, 

 and being of different colors, arranged with much deli- 

 cacy and beauty, it is made into seal-rings, boxes, etc. 



The Opal belongs to the quartz family, is milky, 

 rather than crystalline, brittle, vitreous, and contains 

 water, H. = 5.5 to 6.5, O. = 2.0 to 2.2. Fracture 

 conchoidal, presents internal reflections ; color milk- 

 white, brown-green or gi'ay, nearly translucent, passing 

 into opaque. The first of this class is 



The Precious or Noble Opal. External color usually 

 milky, but within there is a rich play of delicate tints 

 passing into wine color. Was known to the ancients and 

 highly valued by them, was called paideros or child 



