CATALOGUE OF GEMS AND PRECIOUS STONES. 117 



WERNERITE. 



Synonym. — Scapolite. 



Composition. — A complex calcium aluminum sodium chloro-silicate. 



Crystallization. — Tetragonal; pyramidal; habit prismatic. 



Color. — White when pure; may be colored pale violet or pale yel- 

 low by impurities of unknown composition. 



Luster. — Vitreous. 



Hardness. — 5.5; not very durable. 



Specific gravity. — 2.70 ±0.10. 



Optical properties. — Mean refractive index 1.55; double refraction 

 moderate, 0.01. Optically uniaxial, negative. 



The mineral is distinguished by color and optical properties. Oc- 

 curs chiefly in metamorphosed limestone. Because of its peculiar 

 color it is occasionally cut cabochon, but is worth little more than the 

 cost of cutting. 



LIST OF SPECIMENS. 

 CANADA (TEMPLETON, QUEBEC). 



Cabochon, elliptical girdle; yellow; 46.68 carats; 30 by 22 by 11 mm. Isaac 

 Lea collection No. 593 



MADAGASCAR. 



Tsarasaotra Province. 



Brilliant, square girdle; pale yellow; 8.2 carats; 12 by 9 mm. Isaac Lea 

 collection No. 1818 



Step-brilliant; elongated octagonal girdle; pale yellow; 5.77 carats; 12 by 

 10 by 7 mm. Isaac Lea collection No. 1819 



WILLEMITE. 



Composition. — Zinc orthosilicate, Zn 2 (Si0 4 ), with some manganese 

 replacing the zinc. 



Crystallization. — Hexagonal (trigonal), tri-rhombohedral. 



Color. — Colorless when pure, but usually pale green-yellow. 



Luster. — Vitreous; translucent. 



Hardness. — 5.5; not very durable. 



Specific gravity. — 4.10 ±0.10. 



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

 moderate, 0.02; optically uniaxial, positive. 



The high specific gravity of the mineral is a rather characteristic 

 feature, and in color and general appearance it differs from prac- 

 tically every other precious stone. The only willemite thus far 

 found suitable for cutting occurs in the zinc-ore deposit at Franklin 

 Furnace, New Jersey. Most of the material is opaque, or only 

 translucent, and is used as an ore of zinc; but occasional specimens 

 are found which are clear and yield small stones, which are usually 

 cut brilliant. 



4555—22 10 



