MINERALOGY. 425 



opaque, as well as sub-transparent or translucent. Frac- 

 ture flat conchoidal ; crystalline luster subdued and waxy, 

 is of different colors and forms. The gray, white, and 

 brown varieties are called Common Chalcedony ; often 

 found striated, clouded, or with moss-like linear mark- 

 ings. Agate is variegated chalcedony. Moss Agate or 

 Mocha Stone is the variety with dendritic or moss-like 

 delineations. When the colors white and gray alternate 

 with darker shades on flat horizontal planes, it is called 

 Onyx. Found mostly in basaltic formations in the 

 regions of Baden, Oppenau, Black Forest, and at Chem- 

 nitz in Saxony. 



Cornelian is the most valuable variety ; of a clear 

 bright red color, or sometimes brownish passing into yel- 

 low through grayish-red. It loses its color, which, it 

 is supposed, is due to oxyd of iron, by heat. Both 

 chalcedony and cornelian are much used for ornament, 

 as seal rings, brooches, etc. 



Flint is semi-opaque, solid, dense, slightly transpar- 

 ent. Fracture deeply conchoidal ; color gray or smoky 

 yellow, sometimes clouded. Occurs mostly in the chalk 

 formations, namely Champagne and England. From its 

 peculiar structure the working of flint requires great 

 dexterity with the hammer, nevertheless an expert flint 

 mason will commonly make from two to four hundred 

 flint stones per diem. 



Hornstone Chert. Very dense and firm, more brit- 

 tle than flint ; its fracture is splintery ; color outside 

 greenish, red, or brown ; inside foul and dull. The 

 petrified remains of wood are easily recognized in Horn- 

 stone structures. Frequent in the Erzgebirge (Mineral 

 Mountains), Thuringia, and Black Forest. Used for 



