BISILICATES, 253 



marine includes clear beryls of a sea-green, or pale-bluish 01 

 bluish-green tint. 



Composition. Be 3 Al ]8 Si 6 =: Silica 66 8, alumina 19*1, 

 glucina 14*1 = 100. Emerald contains less than' one per 

 cent, of chromium oxide. B.B. becomes clouded, but does 

 not fuse ; at a very high temperature the edges are rounded. 

 Unacted upon by acids. 



Biff. The hardness distinguishes this species from apa- 

 tite ; and this character, and also the form of the crystals, 

 from green tourmaline. 



Obs. The finest emeralds come from Muso, near Santa Fe 

 in New Grenada, where they occur in dolomite. A crystal 

 from this locality, 2J inches long and about 2 inches in 

 diameter, is in the cabinet of the Duke of Devonshire ; it 

 weighs 8 oz. 18 dwts., and is a regular hexagonal prism. A 

 more splendid specimen, but weighing only 6 oz., in the 

 possession of Mr. Hope, of London, cost £500. Emer- 

 alds of less beauty, but of gigantic size, occur in Siberia. 

 One specimen in the royal collection of Russia measures 4J 

 inches in length and 12 in breadth, and weighs 16f pounds 

 troy. Another is 7 inches long and 4 broad, and weighs 6 

 pounds. Mount Zalora in Upper Egypt affords a less dis- 

 tinct variety. 



The finest beryls (aquamarines) come from Siberia, Hin- 

 dostan and Brazil. One specimen belonging to Dom Pedro 

 is as large as the head of a calf, and weighs 225 ounces, or 

 more than 18 J pounds troy ; it is transparent and without a 

 flaw. In 1827 a fine aquamarine, weighing 35 grams, was 

 found in Siberia, which is said to have been valued at 

 600,000 francs. 



In the United States, beryls of enormous size have been 

 obtained, but seldom transparent crystals. They occur in 

 granite or gneiss. One hexagonal prism from Grafton, 1ST. 

 XL, weighs 2,900 pounds and measured 4 feet in length, with 

 one diameter of 32 inches and another of 22 ; its color was 

 bluish green, excepting a part at one extremity, which was 

 dull green and yellow. At Eoyalston, Mass., one crystal has 

 been obtained a foot long, and pellucid crystals are some- 

 times met with. Haddam, Conn., has afforded fine crys- 

 tals (see the figure). Other localities are Barre, Fitchburg, 

 Goshen, Mass. ; Albany, Norwich, Bowdoinham and Top- 

 ham, Me. ; Wilmot, N. H. ; Monroe, Portland, Haddam, 

 Conn. ; Leiperville, Penn. 



