66 MINERALOGY. 



most clear, pellucid pebbles of topaz are cut with facets 

 and set, they appear by daylight precisely like diamonds. 



134. Lapis Lazuli. In this beautiful azure-blue miner- 

 al we have a compound of silica, alumina, soda, lime, iron, 

 sulphuric acid, sulphur, chlorine, and water. It is plain 

 that the silicic acid and the sulphuric acid must form with 

 some of these oxyds a silicate and a sulphate, which are 

 intimately combined together, but how some of these 

 substances are combined we know not. The color is at- 

 tributed to sulphuret of sodium. There are some speci- 

 mens of this mineral whose composition differs somewhat 

 from that given above. 



135. Beryls and Emeralds. A beryl is a silicate of 

 alumina and glucina, while an emerald is the same, col- 

 ored with oxyd of chromium to the amount of less than 

 one per cent. The color is mostly green pale in the 

 beryl, but decided and rich in the emerald. The best 

 emeralds are brought from Granada, where they are 

 found in dolomite ( 104). One, weighing six ounces, 

 cost the owner, Mr. Hope, of London, 500. Emeralds 

 of larger size, but of less beauty, are obtained in Siberia. 

 One in the royal collection of Russia measures four and a 

 half inches by twelve. The finest beryls come from Si- 

 beria, Hindostan, and Brazil. Some beryls of very great 

 size have been obtained in this country, but they are 

 seldom transparent. A hexagonal prism was found in 

 Grafton, New Hampshire, of such enormous size that it 

 weighed 2900 pounds. It is four feet in length. The 

 chrysoberyl is a combination of alumina and glucina, 

 sometimes with a little iron. The color is indicated by 

 the name, which comes from two Greek words, chrysos, 

 yellow, and beryllos, beryl. 



136. Zircon. This mineral, which is a silicate of the 

 earth zirconia, has various colors. The clear crystals are 

 in common use in jewelry. When they are red they are 

 called hyacinths. This variety has some resemblance to 

 the red spinel. Zircon is used in jeweling watches. 



