430 NATURAL HISTORY. 



monds, because they are so easily counterfeited by the 

 substitution of colored glass. 



The Emerald is green, often passing into blue ; trans- 

 parent ; H. = 7.5, to 8.0 ; G. = 2.6, to 2.8 ; of 

 shining vitreous, luster ; found in Pinzgau and the Tyrol, 

 embedded in mica slate. The finest emeralds come from 

 Grenada ; others, of less beauty but gigantic size, occur 

 in Siberia, -and Mount Zalora, in Egypt, affords a distinct 

 variety. The Beryl, which Pliny speaks of as "green, 

 like the sea," and when perfectly transparent, and exhibit- 

 ing clear shades of sky blue or mountain green, is called 

 Aqua-marine, or Noble Beryl, occurs in the form of long 

 hexagonal prisms, imbedded in granite. The finest are 

 brought from Peru. 



Topaz is a perfectly transparent crystal of a reddish- 

 yellow or wine color. H. = 8.0 ; G. = 3.6. Found 

 frequently in South America. The finest crystals are 

 brought from Minas Novas, in Brazil. Sometimes they 

 occur in the form of pebbles, and are found in the rivers 

 of the Southern Continent. This variety is very limpid, 

 and are called gouttes <eau (drops of water). Speci- 

 mens of quartz crystal from Brazil, penetrated by topaz, 

 are not uncommon ; it also occurs in gneiss and granite. 

 The yellow color may be changed to red by heat, but 

 great care is requisite in the process, as the crystal is 

 liable to be broken. Often employed in jewelry, or for 

 polishing hard substances. 



Garnet is deep red, verging into brown ; pellucid, 

 but more frequently perfectly translucent or opaque. H. 

 = 6.5 to 7.51 ; G. = 3.7 to 4.3. Occurs in coarse 

 grains : also in crystals of vitreous luster, when not 

 milky. The pellucid or precious almandine garnets, 

 which bring a high price, are from Ceylon and Greenland. 



