400 STUDIES FOR STUDENTS 



anorthite crystals show twinning according to the Carlsbad law 

 and in the Llano del Inca and Dona Inez meteorites twins 

 according to the albite and pericline laws were found. The 

 mineral is sometimes white and sometimes colorless and in luster 

 varies from dull to vitreous. Inclusions nearly alwa3^s abound 

 and they are generally regularly arranged. The inclusions are 

 chiefly colorless glass, but sometimes brownish glass and opaque 

 grains occur. Analyses of mechanically isolated anorthite have 

 been made which show a composition similar to that of terres- 

 trial anorthite. CaO amounts to about i8 per cent, in these 

 analyses. 



Calculating from analyses Tschermak concludes the feldspar 

 of the stone of Gopalpur to be oligoclase, Lindstrom that of 

 Hessle to be the same and Schilling that of Tennasilm to be 

 labradorite. The presence of plagioclase other than anorthite 

 has been proved by microscopical and chemical examination 

 of other meteorites, but the species have rarely been deter- 

 mined. Such feldspars occur as lath-shaped individuals and 

 as grains and splinters. Inclusions are much less common 

 than in anorthite. Rounded, elongated inclusions referred by 

 Tschermak to chrysolite and bronzite are, however, quite char- 

 acteristic. Gas inclusions seem to be more abundant in the 

 feldspars of meteorites than in any other constituent, though 

 even here they are rare. 



Maskelyiiite. — This is an isotropic, colorless, though becoming 

 milky through alteration, transparent mineral of vitreous luster 

 and conchoidal fracture. Its hardness is somewhat over 6 ; 

 specific gravity 2.65. It has no cleavage but shows occasional 

 irregular cracks and striae similar to those of plagioclase. Inclu- 

 sions of magnetite and augite are arranged in apparent zones. 

 The mineral is slightly decomposed by hydrochloric acid. Thin 

 splinters fuse, but with difficulty. Lath-shaped individuals with 

 rectangular outlines occur, but in most meteorites the mineral is 

 present as minute grains. It forms 22 ^/^ per cent, of the 

 meteorite of Shergotty, the remainder of the meteorite being 

 augite and magnetite. It is also an accessory constitutent in 



