32 JF 1 . A. Genth — " Anglesite" associated with Boleite. 



Art. III. — On the u Anglesite" associated with Boleite, 

 No. 55 ; by F. A. Genth. 



Mallard and Cumenge state in their interesting investiga- 

 tion on boleite* that anglesite, generally covered with a coat- 

 ing of gypsum, of variable thickness, is associated with the 

 boleite from Boleo, Lower California, Mexico. These crystals 

 showed such a peculiar appearance that I thought they de- 

 served a fuller investigation, for which Mr. Clarence S. Benient 

 with his usual liberality, furnished me with excellent material. 



The crystals, from 2 to 20 mm in size are often distorted, but 

 show generally a very common form of anglesite, the planes c, 

 m and I predominating. They are opaque, and of a luster, 

 between vitreous and greasy, their color is from white to bluish 

 white, some show minute blue spots from a slight contamina- 

 tion with boleite. Many crystals have a coating of gypsum or 

 minute scales of the latter implanted, while others are entirely 

 free from it. Sp. gr. = 4*4:01. The material for the analysis 

 was selected with great care and the purest that could be 

 obtained, it gave : 



Molecular ratio. 



PbS0 4 76-16 0-251 2 



CaS0 4 --_ 17-31 0-127 1 



H 2 4-53 0-251 2 



Boleite bv diff. 2-00 



100-00 



This gives the formula : 2PbS0 4 +CaS0 4 4-2H 2 0. As it is not 

 very likely that 2 mol. of PbS0 4 should have crystallized with 

 one mol. of gypsum in exactly the same form as anglesite, we- 

 must come to the conclusion, that the so-called anglesite crys- 

 tals from Boleo are pseud omorphs after a mineral of the com- 

 position : 2PbS0 4 . CaS0 4 , which has not yet been observed in 

 its original condition, but only after the calcium sulphate in 

 it had taken up two molecules of water and changed into gyp- 

 sum which now forms a mechanical mixture with the remain- 

 ing anglesite, from which it can be completely extracted by 

 water. 



The fine powder of two small crystals was treated with 

 water, as long as any precipitate of calcium oxalate could be 

 formed in the filtrate ; a small quantity of lead in the solution 

 was removed by hydrogen sulphide. 



* Bull. Soc. Franc, de Mineralogie, December, 1891. 



