CATALOGUE OF GEMS AND PRECIOUS STONES. 95 



LIST OF SPECIMENS. 

 I'N'ITED STATES. 



North Carolina. 

 Hiddenite, Alexander County: 



Five gems, brilliant, circular girdle; dark red, nearly opaque; total 

 weight, 2.93 carats; average size, 5 by 3 mm No. 457 



SAMARSKITE. 



Composition. — Complex iron, yttrium, and uranium columbate. 



Crystallization. — Orthorhombic. 



Color. — Black. 



Luster. — Submetallic; practically opaque. 



Hardness. — 5.5; not durable. 



Specific gravity. — 5. 70 ±0.50. 



Optical properties. — Indeterminate. 



Methods of identification. — Can be recognized more or less definitely 

 by the luster and specific gravity, but can be distinguished from 

 closely related minerals only by analysis. 



Occurrence. — Occurs in pegmatite rocks and is sometimes cut bril- 

 liant, and is used in place of jet, but is of no greater value than 

 cost of cutting. 



LIST OF SPECIMENS. 



UNITED STATES. 



North Carolina. 

 Mitchell County: 



Brilliant, circular girdle; black, opaque; 6.55 carats; 12 by 6 mm. Isaac 

 Lea collection No. 588 



Sapphire. — See under Corundum. 

 Sardonyx. — See under Chalcedony. 

 Satelite.— See under Serpentine. 

 Satin spar. — See under Gypsum. 

 Selenite. — See under Gypsum. 



SERPENTINE. 



Varieties. — Williamsite, satelite, precious serpentine, verde-antique. 



Composition. — Hydrous magnesium silicate, H 2 Mg 3 Si 2 9 . 



Crystallization. — -Probably monoclinic, but never found in good 

 crystals. 



Color. — Normally green, owing to a small amount of ferrous iron 

 replacing the magnesium. 



Luster. — Vitreous or somewhat greasy; translucent. 



Hardness. — 4; does not wear well. 



Specific gravity. — 2.5 ± 0.2. 



Optical properties. — Mean refractive index 1.53; double refraction 

 very weak. 



