360 Description and Analysis of Pickeringite. 



Art. XIX. — Description and Analysis of Pickeringite, a native 

 Magnesian Alum ; by Augustus A. Hayes. 



This mineral occurs in masses, which are composed of long 

 parallel fibres, easily divisible, and generally affords rhombic pris- 

 matic forms. There are numerous cross-fissures, and the fracture 

 at these is even. Transparent to translucent, having the satin- 

 like lustre of the finest specimens of satin spar, which it much 

 resembles. Color white, but when viewed in the direction of 

 the fibres, pale rose red, or a delicate green. Taste, like that of 

 alum. Sp. gr. 1-78 to 1-80. In dry air it effloresces, in moist air 

 it attracts water, and the fibres become flexible. It is soluble in 

 cold water, without residue, and the solution has an acid action. 



By chemical analysis, it affords 



Water of crystallization, .... 45-450 



Sulphuric acid, 

 Alumina, 



Magnesia, 



36 322 

 12130 

 4-6S2 

 0-430 

 0126 

 0-604 

 0-256 



Protoxides of manganese and iron, 



Lime, 



Hydrochloric acid, .... 

 Loss, ...... 



100000 

 Neglecting the substances, evidently existing in the state of 

 mixture with the double salt of alumina, its chemical formula is 



MgS-fAlS 3 +22H.* 

 In the analysis, bicarbonate of ammonia was used for precipi- 

 tating the alumina and retaining the larger part of the magnesia, 

 in solution with the sulphuric and hydrochloric acids. The pre- 

 cipitate was ignited, so long as it lost weight ; it was then redis- 

 solved in strong nitric acid, and its solution was decomposed by 

 a large excess of potash solution. The hydrates, insoluble in a 



* The water in the above analysis approaches so near 24 atoms, that this is prob- 

 ably the amount contained, in which respect it will then conform to the general for- 

 mula for the alums, RS-f-AlS3-f24H[. The exactformula would be (Mg,Mn,Fe) 



S-f- ikl S 3 -J-24H, which, excepting the iron, is identical with that of an African 

 alum analyzed by Stromeyer. (See Rammelsberg's Handworterbuch, &c. Vol. I, 

 p. 10 ; also Dana's Mineralogy, 2d edition, 1844, p. 554.) — Eds. 



