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PEOCEEDINGS OF THE NATIOISTAL MUSEUM 



VOL. 74 



prism faces m(llO) are extended to a point eliminating the pinacoid 

 face h (010). The optical properties are the normal ones for celestite, 

 and the mineral gives the characteristic blowpipe reactions and 

 strontium flame. The crj^stal measured gave the following angles: 



Even the smaller crystals are somewhat imperfect and do not give 

 good measurements. The minerals of the veins do not penetrate the 

 ■adjacent sandstone which appears unaltered and is scarcely cemented. 



PALIGOKSKITE 



Paligorskite is an old name used to indicate matted fibrous and 

 very light felted material of the character of " mountain cork " when 

 in masses and " mountain leather " when in thin sheets. Most of the 

 material so designated may have been merely a structure phase of 

 ordinary fibrous or asbestiform tremolite or possibly in some cases 

 serpentine of the chrysolite variety. Much of the material included 

 under this classification has been known to contain considerable 

 water and for this reason paligorskite has been considered an altered 

 and hydrated asbestiform amphibole. Fersmann ^^ in describing a 

 specimen of the mineral from Eussia attempted to interpret the col- 

 lected analyses by postulating a " paligorskite group " made up of 

 variable isomorphous mixtures of two end members, namely : 



Parasepiolite, (A)HsMg2Si30i2. =2Mg0.3Si02.4H.O. 



Paramontmorillonite, (B) H2AUSi40i2.5H20=Ah03.4Si02.7H20. 



Like too many theories as to the chemical constitution of the silicate 

 minerals, this appears to lack sufficient proof to make it readily ac- 

 ceptable and, inasmuch as many of the analyses are old and not made 

 upon microscopically studied material they doubtless include both 

 inaccurate analytical work and analyses made on inhomogeneous 

 materials. It seems certain that manv mountain corks are reallv 



'3 A. E. Fersmann. Min. Inst. Univ. Moscow, 

 pp. 255-274, Chem. Abstr., vol. 2, p. 403. 



Bull. Acad. Imp. St. Petersburg, 1908. 



