384 Reports and Proceedings — Mineralogical Society. 



II. — Mineralogical Society. 



June 18, 1912.— Dr. A. E. H. Tutton, Vice- President, iu the Chair. 

 T. V. Barker : The Isomorphism of the Acid Tartrates aud 

 Tartaremetics of Potassium, Rubidium, and Caesium. The corrections 

 of previous measurements of the three acid tartrates have been con- 

 firmed, and in addition the molecular volumes have been calculated ; 

 the properties of the three salts are found to exhibit a regular pro- 

 gression in order of molecular weight. Solutions of caesium tartar- 

 emetic on evaporation yield syrups which refuse, to crystallize, even 

 when inoculated with a fragment of a salt presumably isomorphous 

 Avith it. The rubidium salt, however, affords good crystals, which, 

 contrary to previous observations, j'ield measurements almost identical 

 with those of the corresponding thallium and ammonium salts, and 

 fairly close to those of the potassium salt ; there is therefore every 

 indication that this group of salts presents relationships similar to 

 those obtained by Tutton in the sulphate and selenate series. The 

 eutropic character of potassium, rubidium, and caesium compounds 

 was discussed in detail, aud it was shown that not only the cases in 

 which they exhibit isomorphism, but also those in which isopoly- 

 morphism is met with, unmistakably point to the intermediate position 

 of rubidium.— W. F. P. McLintock and T. C. F. Hall : On the Topaz 

 and Beryl from the Granite of Lundy Island. The granite consists 

 essentially of quartz, orthoclase, albite, biotite, and muscovite, 

 cordierite and garnet also being present. Well-shaped crystals of 

 topaz and beryl line druses in the granite, and are associated with 

 tourmaline, fluor, and apatite. The felspar of the druses is frequently 

 kaolinized, and the orthoclase has in every case been affected first. 

 It is suggested that carbonic acid was the principal agent in effecting 

 the change, and that the alkaline carbonates produced attacked the 

 topaz, the crystals of which are invariably etched, and are sometimes 

 altered to a white secondary mica ; the formation of the fluor is 

 ascribed to the same period. — R. H. Solly : On the Rathite Group. 

 The characters of the members of the group were discussed, and the 

 similarity of angles in the prism zone was pointed out. — Dr. G. T. 

 Prior: On the Minerals of the El J^akhla el Baharia Meteorite. This 

 meteoric stone consists of a fairly coarse-grained aggregate of green 

 augite, a highly ferriferous brown olivine, and a little interstitial 

 felspar. The augite, which constitutes about three-quarters of the 

 stone by weight, has a chemical composition approximating to a 

 formula 3 Ca Si O3 . 3 Mg SiOj . 2 Fe Si 0,, , a mean refractive index 

 1-686, double refraction 0035 about, and optic axial angle 2E = 89°. 

 The olivine closely approaches hortonolite, except that it contains no 

 manganese ; it has a chemical composition represented by the formula 

 2 Fco Si O4 . Mg.2 Si O4 , a mean refi'active index r785 about, double 

 refraction 0-050 about, and optic axial angle 2V = 87°. — J. B. 

 Scrivenor : Note on the occurrence of Cassiterite and Struverite in 

 Perak. The extent of the occurrence of struverite was discussed, and 

 specimens illustrating uncommon occurrences of tin-ore were exhibited 

 and described. 



