TOURMALINE (ACHROITE— RUBELLITE) 369 



as far as precious tourmaline is concerned, unimportant. The precious varieties are 

 found almost exclusively in the rocks first mentioned, mainly in granite, and especially 

 in its more coarsely crystallised variety known as pegmatite. The light-coloured crystals 

 are attached to the walls of drusy cavities in such rocks, while in other druses of the 

 same rock-mass there may be crystals of different colours, including black. Typical 

 examples of this mode of occurrence may be seen in the granite of San Piero, in the 

 island of Elba, of Penig, in Saxony, and specially at Paris, in Maine, U.S.A. Other 

 localities, in particular those at which stones suitable for cutting are found, will be mentioned 

 later. Darker crystals, brown, blue, or black in colour, are often found embedded in the 

 rock itself, black crystals being met with very frequently. Crystals of tourmaline are 

 often weathered out of their granitic mother-rock and are then to be found in sands and 

 gravels. It is from such deposits that the finest gems are derived, these being collected 

 along with other precious stones at various localities, especially in Brazil and Ceylon. 



All varieties of tourmaline, so long as they are transparent and finely coloured, are 

 suitable for cutting as gems, and, as a matter of fact, material of the most varied character 

 is applied to this purpose. The colourless achroite is little used, and pale-coloured stones 

 generally are not much prized. Stones of a full red, green, blue, or brown-colour are most 

 admired, red stones being the most valuable, green the most abundant, and blue and brown 

 the least important. 



Tourmaline is rarely cut as a brilliant, the table-cut and a low step-cut being more 

 generally adopted. The colour of cut stones is sometimes improved by the use of a suitable 

 foil. Other than the frequently occurring fissures, already mentioned, tourmaline exhibits 

 but few faults, enclosures of foreign substances, for example, being quite exceptional. 



Each of the colour-varieties of precious tourmaline will be now treated of in some 

 detail. 



COLOUBIiESS TOURMALINE or ACHROITE occurs as crystals, which are 

 perfectly, or almost, water-clear, but, as a rule, these are too small to give gems of nmch 

 value. The acicular crystals are found, together with tourmaline of other colours, in the 

 island of Elba, also as fine crystals associated with green tourmaline in the dolomite of 

 Campo-longo, in Switzerland, and at some other localities, but everywhere as a rarity. 

 Crystals of colourless tourmaline in some quantity and of moderate size have been found 

 perhaps only in the neighbourhood of Richville, near De Kalb, St. Lawrence County, in the 

 State of New York, where they occur, as in Elba, attached to the walls of drusy cavities in 

 granite. 



Achroite is readily distinguished from all other colourless and transparent stones by its 

 specific gravity, which is 3-022, so that it just sinks in liquid No. 3 (sp. gr. = 3"0) and floats 

 in liquid No. 2, which is pure methylene iodide (sp. gr. = 3'3). Phenakite, colourless beryl, 

 and rock-crystal float in the former liquid, while diamond, colourless topaz, spinel, sapphire, 

 and zircon all sink in the latter. In beauty of appearance, however, achroite has nothing 

 to distinguish it from many other coloui'less and transparent stones, except in some cases its 

 fine lustre. In common with all other varieties of tourmaline it may be distinguished from 

 glass imitations by its double refraction and its hardness, as well as under certain conditions 

 by its electrical properties. 



RED TOURMALINE or RUBELLITE (siberite) may be of various shades of colour, 

 from pale rose to dark carmine-red, sometimes tinged with violet. The colour may be so 

 like that of certain rubies that it is difficult, even for an expert, to discriminate between 

 these stones on mere inspection. The same similarity in colour may also exist between this 

 variety of tourmaline and certain specimens of balas-ruby (spinel) and rose topaz. From all 



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