618 PHYSIOGRAPHY". CLASS II. 



Oxide of Tantalum 0-27 0-00. 



Oxide of Chrome 0-00 0-30. 



Lime 0-00 0-25. 



In a strong heat of the blowpipe, the edges are rounded 

 off', and a shapeless vesicular scoria is produced. Trans- 

 parent varieties become milky. It is dissolved by borax. 



3. Rhombohedral Emerald occurs in imbedded crystals 

 in various rocks, and in implanted crystals in veins, and 

 also in beds. It is associated with Felspar, prismatic Topaz, 

 &c., or with pyramidal Tin-ore, and other minerals com- 

 monly found with the latter species. It occurs also in frac- 

 tured crystals and rolled masses in secondary repositories. 



4. The finest crystals of emerald-green colours, or the 

 real Emerald, comes from Peru, where it forms druses 

 with rhombohedral Lime-haloide, and occurs, according to 

 HUMBOLDT, in veins traversing hornblende slate, clay- 

 slate, and granite. Sometimes rhombohedral Quartz and 

 hexahedral Iron-pyrites are found along with them. Less 

 distinct varieties, generally of muddy emerald -green colours, 

 are found imbedded in mica-slate in the valley of Heubach, 

 district of Pinzgau, Salzburg. The ancients procured their 

 emeralds from Egypt. The localities however had been 

 lost, till of very late years they have been re-discovered 

 in Mount Zalara in Upper Egypt, where this species oc- 

 curs in granite and mica-slate. Precious Beryl is chiefly 

 found in Siberia and Brazil. In Siberia it occurs in the 

 granitic district of Nertschinsk, also in the Uralian and 

 Altai mountains, often in very large crystals, probably in 

 veins ; in Brazil it is found in fractured crystals in the 

 sand of rivers ; thus likewise it occurs in Aberdeenshire 

 in Scotland, but has lately also been found engaged in the 

 granite of Rubislaw quarry near Aberdeen. Varieties, 

 both of precious and of common Beryl, are met with near Li- 

 moges in France, near Zwiesel on the Rabenstein in Bava- 

 ria, at Finbo and Broddbo near Fahlun in Sweden, in im- 

 bedded crystals and massive varieties ; in some of the tin- 

 mines of Saxony and Bohemia. It occurs in small quan- 



