474 Wiltshireite : a New Mineral. 



(. r >) Similar peculiarities in the saturation curves for the 

 positive ions of aluminium phosphate and lime are also 

 noticed. 



(6) The negative ions from these three sources show no 

 such peculiarities. 



I have to thank Dr. R. S. Willows for the use of the 

 Cass Physical Laboratory and much kindly advice and 

 assistance. 



XL VII. Wiltshireite : a New Mineral. 

 By Prof. W. J. Lewis, M.A., F.B.S.* 



DURING a recent visit to Binn (Valais) I obtained, 

 amongst several other interesting specimens, one which 

 gives on measurement a series of angles which leave little 

 doubt that it has not been hitherto described. It is associated 

 with a crystal of sartorite in a cavity in the well-known 

 dolomite; and from its position it is probably of more recent 

 origin. Its colour is for the most part tin- white, but a few 

 of the facets have a russet tarnish. The crystals are small 

 but piled on one another in almost absolutely parallel 

 orientation, and the same facet on separate individuals gives 

 in many cases a distinct single image, although some of the 

 most important cases give two images separated by some ten 

 minutes. So far only a crystallographic determination can 

 be made, and its chemical composition must be left until 

 further specimens are found, though it is highly probable 

 that it is a lead sulpharsenite. 



The faces 201, 302, 101, 001, and 101 are smooth and bright, 

 and give for the most part good images; they are all very 

 small end-facets. The hemi-pyramids which occur in two 

 homologous zones symmetrical to a symmetry-plane are also 

 smooth and bright; and single images were got from several 

 distinct and separate facets on different parts of the specimen. 

 The faces in the vertical zone 100, 310, 320, 120, and 010, 

 are strongly striated parallel to their edges, along which the 

 crystals are elongated; they give good images in zones which 

 likewise include pinakoids and hemipyramids, but direct 

 observations over the vertical edges give very indifferent 

 measurements. 



The crystal belongs to the oblique system, and its elements 



Communicated by the Author. 



