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TAB. CII. 



SILEX Quartzum, crystallizatum. 



Crystallized Quartz; Cairn Gorum Crystals. 



Class 2. Earths. Order 1. Homogeneous. 

 Gen. 4. Silex. Spec. I. Quartzum. 



Syn. Quartz hyalin plagiedre. Haiiy, v. 2. 413. 



Quartz hyalin rhombifere. Haiiy, v. 2. 413. 



C-airn Gorum Crystals have been known for some years, 

 and are said to have first caused the lapidaries to settle in 

 Aberdeen, where they have been constantly employed in 

 cutting them for seals, ring-stones, &c. They are per- 

 haps of the oldest formation, and are found of various de- 

 grees of transparency, and sometimes are coloured yellow 

 or brown. When of a deep colour they are esteemed as 

 topazes *, and if clear and large are sold at a high price. 

 The brown ones are also valued if clear; but when of a bad 

 yellow, or muddy brown, the lapidaries have recourse to 

 their art, and prove them to be rock crystals, by dissipating 

 their colour, and giving them a transparent lustre. See p. 88. 

 This specimen is remarkable for the face s of Haiiy (i. e. 

 the little narrow face in the middle of the right-hand out- 

 line, which is often more regularly rhomboidal), being a 

 truncation of the solid angle of the base of the pyramid ; 

 and the oblique face on the column, which is just below it, 



* Topazes are found in the Brazils, &c. 

 VOL. II. B 



