BERYL. 



This mineral species includes a number 

 of varieties which are highly valued as 

 gems. These are, besides Beryl itself, the 

 gems emerald, aquamarine and golden 

 beryl. Chrysoberyl, it may be noted, is 

 not a variety of Beryl, but a distinct spe- 

 cies. 



While these gems all differ in color, 

 they are the same mineral and are practi- 

 cally identical in composition, hardness 

 and other properties. In composition 

 they are a silicate of aluminum and glu- 

 cinum, the percentage being, for normal 

 beryl, 67 per cent of silica, 19 per cent of 

 alumnia and 14 per cent of glucina. 



The beautiful green color of the emer- 

 ald is probably due to a small quantity of 

 chromium which it usually contains, 

 though some authorities believe organic 

 matter to be the coloring ingredient. To 

 what substance the other varieties of the 

 species owe their color is not known. 



In hardness the varieties of Beryl differ 

 little from quartz, the hardness being 7.5 

 to 8 in the scale of which quartz is 7. 

 They are somewhat inferior therefore to 

 such gems as topaz, sapphire and ruby in 

 wearing qualities, although hard enough 

 for ordinary purposes. 



The specific gravity of Beryl is also 

 about like that of quartz, ranging from 

 2.63 to 2.80 ; the specific gravity of quartz 

 being 2.65. The varieties of Beryl are 

 therefore relatively light as compared 

 with other gems. 



Beryl crystallizes in the hexagonal sys- 

 tem. It usually occurs as six-sided 

 prisms, commonly terminated by a single 

 flat plane, but sometimes by numerous 

 small planes giving a rounded effect and 

 occasionally by pyramidal planes which 

 cause the prism to taper to a sharp point. 



The crystals sometimes grow to enor- 

 mous size, exceeding those of any other 

 known mineral. Thus, one found in 

 Grafton, New Hampshire, was four and 



one-quarter feet in length and weighed 

 two thousand nine hundred pounds. An- 

 other in the same locality is estimated 

 to weigh two and one-half tons. 

 In the museum of the Boston So- 

 ciety of Natural History and in the 

 United States National Museum are ex- 

 hibited single crystals also of great size. 

 That in Boston is three and one-half feet 

 long by three feet wide and weighs sev- 

 eral tons. That in the National Museum 

 weighs over six hundred pounds. 



None of these crystals are of a high 

 degree of purity or transparency, but the 

 crystal planes at least of the prisms are 

 well developed. 



Beryl crystals have no marked cleav- 

 age except a slight one parallel with the 

 base. Where broken, the surface shows 

 what is called conchoidal fracture, i. e. it 

 exhibits little rounded concavities and 

 convexities resembling a shell in shape. 



The mineral is quite brittle. Some 

 emeralds even have the annoying habit of 

 breaking of their own accord soon after 

 removal from the mine. This can be 

 prevented by warming them gradually 

 before exposing them to the heat of the 

 sun or other sudden heat. 



Beryl and its varieties, like tourmaline, 

 are dichroic, i. e. the stones exhibit differ- 

 ent colors when viewed in different direc- 

 tions. This dichroism can sometimes be 

 observed by the naked eye, but often not 

 without the aid of the instrument known 

 as the dichroscope. When seen it fur- 

 nishes a positive means of distinguishing 

 a true stone from any glass imitations. 



The varieties of Beryl have none of 

 the brilliancy of the diamond and there- 

 fore depend wholly on their body colors 

 and their lustre for their beauty and at- 

 tractiveness. Fortunately they exhibit 

 these qualities as well by artificial light as 

 by daylight. 



Ordinary Beryl is a mineral of com- 



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