140 Reports and ProceecU)tgs — Mineralogical Society. 



MlNEllALOGICAL SoCIEXr. 



January 23. — Professor W. J. Lewis, F.R.S., President, in tlie Chair. 



Miss M. W. Porter and Dr. A. E. H. Tutton : The Relationship 

 between Crystalline Form and Chemical Constitution : The Double 

 Chromates of the Alkalies and Magnesium. The investigation of the 

 crystals of ammonium-magnesium chromate containing 6 HoO, and 

 of those of the analogous salts containing rubidium and csesium (the 

 formation of the corresponding potassium salt being impossible), shows 

 not only that the double chromates belong to the same monoclinic 

 series as the double sulphates and selenates previously investigated by 

 Dr. Tutton, but that their mutual relationships are precisely parallel 

 to those atforded by the other groups of the series. The rubidium and 

 caesium salts exliibit the same progressive changes of morphological 

 and pliysical properties in the same direction as the rubidium and 

 caesium salts of all the other groups investigated, so that if the 

 potassium salt could be prepared the three salts vs^ould undoubtedly 

 form a eutropic group progressive in properties in accordance with the 

 atomic weights of the three alkali metals, and it is even possible to 

 predict the properties of the missing potassium salt. As in all the 

 other cases, the ammonium salt is isomorphous and not eutropic. 

 Moreover, the double chi'omates are isomorphous and not eutropic 

 with the eutropic sulphates and selenates. — Professor W. J. Lewis : 

 On a lead-gi'ey Sulpharsenite from Binn, probably Liveingite. The 

 crystals have two jirominent zones mutually inclined at 90"^, the one 

 markedly oblique and the other ])rismatic in symmetry. Assuming 

 oblique symmetry, the face-symbols are very high numbers; assuming 

 anorthic symmetry, they are simple, but the crystals possess several 

 relations characteristic of oblique symmetry, and twinning, though 

 undoubtedly occurring, is not a satisfactory' explanation. — R. H. Solly 

 and Dr. G. JF. H. Smith : A new Anorthic Mineral from the Binnental. 

 Since no further crystals have come to light similar to the five minute 

 ones found in 1902 by Mr. Solly on a crystal of, probably, rathite, 

 they have recently been remeasured. They are lead-grey and their 

 streak is chocolate in colour, and they are therefore probably 

 a sulpharsenite of lead. jSTo axes or plane of symmetry were observed, 

 and the symmetry is therefore anorthic. The fundamental constants 

 are a : I : c = ()-9787 : 1 : 11575 ; « = 116' 53^-', /3 = 85° 12', 

 7 = 113" 44i'; 010: 001 = 62° 41', 001 : 100 == 83° 4^', 100 : 010 = 

 65° 46' ; and about twenty-one forms were observed, of which the 

 most prominent are 100, 010, 001 , 1 10, 1 11, 111.— Dr. A.Hutchinson: 

 On Coleraanite and Neocolemanite. By a slight change in the orien- 

 tation adopted for the crystals of the latter mineral its crystallographic 

 and optical pi'operties can be brought into harmony with those of the 

 former. This can be effected by a rotation of the crystal through 

 180°, about the normal, to the face 001, 100 of neocolemanite, tlien 

 coinciding with 201 of colemanite. — Dr. A. Hutchinson and Dr. A. E. H. 

 Tutton : Further observations on the Optical Characters of Gypsum. 

 With the aid of new appai'atus by which the section-plate of gypsum 

 perpendicular to the first median line can be surrounded during 

 observations of the interference hgure by flowing hot water, of which 



