CATALOGUE OF GEMS AND PRECIOUS STONES. 67 



HYPERSTHENE. 



Variety. — Bronzite. 



Composition. — Magnesium and iron metasilicate, (Mg, Fe) Si0 3 . 



Crystallization . — ( )rthorhombic. 



Color. — Black, with bronze internal color; pleochroism distinct 

 under the microscope. 



Luster. — Submetallic. 



Hardness. — 5.5; not very durable. 



Specific gravity. — 3.50 ±0.20. 



Optical properties. — Mean refractive index, 1.70; double refraction 

 moderate, about 0.01; biaxial, negative. 



Hypersthene and bronzite are members of the pyroxene family and 

 are common constitutents of certain types of volcanic rocks. They 

 occasionally afford material that can be cut and are of interest but 

 of little use as precious stones; are sometimes cut cabochon as a 

 curiosity. 



LIST OF SPECIMENS. 



NORWAY (FREDRIKSVARN). 



Cabochon, elliptical girdle; black with bronze luster; 15.67 carats; 22 by 

 16 by 5 mm No. 422 



IOLITE. 



Synonyms. — Cordierite, dichroite, "water-sapphire." 



Composition. — Magnesium aluminum metasilicate, Mg 4 Al 8 O 6 (SiO 3 )i . 



Crystallization. — Orthorhombic. 



Color. — Blue, usually somewhat smoky; strongly pleochroic, from 

 yellow to blue. 



Luster. — Vitreous ; transparent. 



Hardness. — 7; a durable stone. 



Specific gravity. — 2. 65 ±0.05. 



Optical properties. — Mean refractive index, 1.54; double refraction 

 weak, 0.008; optically biaxial, negative. 



The mineral occurs in pegmatite and in metamorphic rocks. 

 When cut in such a direction that the blue color shows at the top, 

 it is used to some extent as a precious stone. Its value is slight. 



LIST OF SPECIMEN'S. 

 BAVARIA (BODENMAIS). 



Rectangular block; violet-blue to yellow-gray; 7.45 carats; 11 by 9 by 6 mm.. No. 5S6 



CEYLON. 



Step-brilliant, rectangular girdle; light blue; 6.76 carats; 14 by 12 by 4 mm. 



Isaac Lea collection No. 584 



Step, rectangular girdle; pale violet-blue; 1.38 carats; 9 by 7.5 by 3 mm No. 585 



