440 MINERALOGY 



ground to a powder, but has been displaced by the much cheaper 

 artificial product, formed by the fusion of kaolin, sodium carbonate, 

 and sulphur at comparatively a low temperature, below 700, as 

 these minerals decompose or are unstable above that temperature. 



IOLITE 



lolite. Cordierite; Dichroite; H 2 (Mg . Fe) 4 Al 8 Siio0 3 7 ; MgO = 



10.2, FeO = 5.3, A1 2 O 3 = 33.6, Si0 2 =49.4, H 2 O = 1.5; Ortho- 

 rhombic ; Type, Didigonal Equatorial ; a : b : c = .5871 : 1 : .5585 ; 

 100 A 110 = 30 25'; 001 A 101 =43 34'; 001 A Oil =29 11'; 

 Common forms, c (001), a (100), b (010), m (110), d (130), s (112) ; 

 Twinning plane m forming pseudo-hexagonal shapes; Cleavage, 

 brachypinacoidal distinct, a and c less so; Brittle; Fracture, 

 conchoidal ; H. = 7-7.5 ; G. = 2.6-2.66 ; Color, shades of blue or 

 smoky ; Streak, white ; Transparent to translucent ; Pleochroism 

 very strong, a bluish, b yellow, c blue; a = 1.532; |3 = 1.536; 

 y = 1.539; -y - a = .007; Optically ( - ); Axial plane = 100; 

 Bx a = c ; 2 V = 39 32' but variable. 



B.B. Becomes opaque, and fuses with difficulty at 5.5. The 

 powdered mineral heated very hot in the closed tube yields water. 

 Partially decomposed in acids. 



General description. Crystals are short prismatic in habit, 

 pseudo-hexagonal from twinning ; more often it occurs granular or 

 massive. lolite occurs as a constituent of igneous rocks, but is 

 more characteristic of schists, gneisses, and contact metamorphosis, 

 where it is associated with tourmaline, biotite, garnets, sillimanite, 

 quartz, and the plagioclases. It is widely distributed in the gneisses 

 of Connecticut, Massachusetts, and New Hampshire. In sections 

 it appears very much like quartz, but is slightly pleochroic in thin 

 sections and is biaxial. The variety cerasite from Japan has a large 

 number of inclusions symmetrically arranged, as in andalusite or 

 chiastolite. It decomposes easily, forming by hydration a series 

 of compounds, as fahlunite, praseolite, gigantolite, and with the 

 addition of iron and alkalies, pinite or mica is formed. 



NEPHELITE 



Nephelite. Nepheline ; Elaeolite, (Na . K) AlSi0 4 , usually 

 written K 2 Na 6 Al 8 Si 9 3 4 ; K 2 O = 7.7, Na^O = 15.1, A1 2 3 = 



33.3, Si0 2 = 44; Hexagonal; Type, Hexagonal Alternating; 

 c = .8389; 0001 A lOfl = 44 5'; Crystal forms, c (0001), 



