CATALOGUE OF GEMS AND PRECIOUS STONES. 81 



PYRITE. 



Synonym. — Sulphur-diamond. 



Composition. — Iron disulphide, FeS 2 . 



Crystallization. — Isometric. 



Color. — Brass yellow. 



Luster. — Metallic, opaque. 



Hardness. — 6; can not be cut by a knife; fairly durable. 



Specific gravity. — 5 ±0.05. 



Optical properties. — Indeterminate. 



Miscellaneous properties. — Some varieties are easily decomposed by 

 moist air, losing their luster and gradually falling to pieces. The 

 color and luster are characteristic. 



Pyrite is a very unstable mineral but occurs in a great variety of 

 geological situations. It is used usually without cutting or polishing, 

 as the natural luster is very brilliant. Being a very common mineral 

 it is sold for little more than the cost of trimming and mounting. 



LIST OF SPECIMENS. 



UNITED STATES. 



Pennsylvania. 

 Schuylkill County: 



Two pieces, one oval, one rectangular girdle; brass yellow; 20 by 14 by 



7 and 13 by 10 by 7 mm. Gift of J. W. Beath No. 678 



Pyrope.— See under Garnet. 



PYROXENE, variety DIOPSIDE. . 



Composition. — Calcium magnesium meta-silicate, CaMg(Si0 3 ) 2 . 



Crystallization.- — Monoclinic. 



Color. — Pale green, owing to the presence of a small amount of 

 ferrous iron. 



Luster. — Vitreous. 



Hardness. — 6 ; not very durable. 



Specific gravity. — 3.25 ± 0.1 . 



Optical properties. — Mean refractive index, 1.71; double refraction 

 strong, 0.03; optically biaxial, positive. 



The mineral occurs in metamorphosed limestones. The color, 

 as a rule, is not attractive enough to make it of much importance 

 as a precious stone. 



LIST OF SPECIMENS. 

 CANADA (RENFREW COUNTY, ONTARIO). 



Step-brilliant, rectangular girdle; pale green; 1.7 carats; 7.5 by 7 by 4.5 mm. 



Isaac Lea collection No. 575 



TYROL. 



Step, rectangular girdle; very pale yellow; 1.65 carats; 9 by 7 by 3 mm No. 576 



Step-brilliant, rectangular girdle: deep yellow-green; 1.33 carats; 7.5 by 6 



bv 4 mm No. 577 



