SI] l< \TI .S. TITAN 'ATl-iS. KTC. 



453 



- pl.ni. IDll = Common forms, a (1120), r (1011), s (0221). 

 rliniiiliolir.lr.-il perfect; Brittle; Fracture, conchoidal ; 

 H. = 5; G. = 3.28-3.35; Color, emerald green ; Streak, pale 

 mini: Luster, vitreous ; Transparent to translucent ; o> = 1.667; 

 c = 1.723; -o> = .056 Optically (+). 



B.B. Infusible, but blackens and decrepitates. Reduced on 

 coal with soda and a little coal dust yields metallic copper. 

 ( lelatini/es \\ith HC1. Yields water in the closed tube. 



General description. Crystals arc prismatic in habit, combina- 

 tions of the hexagonal prism of the second order, terminated by the 

 rhombohedron s or several rhombohedrons of the same series. 

 The rhombohedron x (1231) also appears on some specimens, fix- 

 ing the symmetry as hexagonal alternating. 



Dioptase is a rare mineral, found only in a few localities and then 

 in very small amounts. The finest specimens, some of which 

 are nearly an inch in length are obtained in a limestone near 

 Altyn-Tiibe, Siberia. Occurs at Copiapo, Chili, and in the Clifton 

 Mine Graham Co., Arizona. 



When the crystals are clear and flawless, they are cut and 

 polished as a gem. 



SCAPOLITE GROUP 



The chemical composition is variable, as the scapolite group, like 

 the plagioclase feldspars, is formed by two end members, meion- 

 ite, Ca4 A1 6 Si O 25 (me) and marialite, Na 4 Ala Si 9 O 24 Cl, (ma) ; 

 these two species form isomorphous mixtures in all proportions, 

 and therefore in composition the series passes uninterruptedly 

 from one extreme to the other. 



Meionite me + mao to me 3 + mai 0.4393 



Wernerite 

 Mizzonite 



me 2 + mai to mei + mai 0.4384 

 + mai to mex + ma 3 0.4424 



Marialite mei + mas to me + ma 0.4417 I . ' 



1.594 

 583 

 1.570 

 1.567 

 1.562 

 5545 



1.557 

 1.554 

 1.547 

 1.550 

 1.546 



0.037 

 0.029 

 0.023 

 0.017 

 0.016 



1.5417 0.013 



WERNERITE 



Wernerite. Calcium aluminium orthosilicate, 

 CaO = 25.1, A1 2 O 3 = 34.4, SiO 2 = 40.5; Tetragonal; Type, 



