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Topaz

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216 GEMS.
 
 

 
 
The Oriental topaz is a clear, coloured corundum, of a very bright golden-yellow colour, having a specific gravity of 4. It has double refraction, although in a small degree. It is found in crystals, which are generally round, like those of other corundums, but sometimes it shows its primitive form, which is a quadrangular prism.
Its hardness equals that of other corundums. It is found at Peru, Ceylon, and in various other parts of India.
With respect to value, it never equals the ruby, sapphire, and emerald. Sometimes it contains little grains which shine like those of the aventurine, but these rather diminish than increase its value.
There is a beautiful topaz in the mineralogical cabi­net of Paris 0.023 mètres long, and 0.014 mètres wide.
The Western topaz is divided into four different kinds, viz., Brazilian, Saxon, Mexican, and Siberian.
The Brazilian topaz, which is now most valued next to the Oriental, is generally of a fine, clear deep yellow ; it has such a particular appearance that it is easily recognizable.
One of its physical qualities, by which its nature may even better be determined is, that when somewhat heated it acquires electricity, which it preserves some­times for thirty hours.
It cuts rock crystal deeply, and its specific weight is 3-52. The most extraordinary of its peculiarities is that of changing colour from yellow to a pink shade when warmed to a certain temperature. This discovery
 
 

 
     
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