188 Reports c& Proceedings — Mineralogical Society. 



MiNERALOGICAL SoCIETY. 



January 20, 1920.— Dr. A. E. H. Tutton, F.R.S., Past President. 



in the chair. 



Dr. E. S. Simpson: " Gearksutite at Gingin, Western Australia." 

 The mineral, which occurs in Cretaceous greensand, is considered 

 to have a composition corresponding to the formula CaFo . A1F(0H)3 . 

 H2O, and to have originated from the interaction in situ of 

 fluorapatite, gibbsite, and carbonated water. — C. E. Barrs : " Fibro- 

 ferrite from Cyprus." Analysis of material from Skouriotissa, 

 Cyprus, gave the following result : Fe.,03 31-36, SOo 30-95, H.O (by 

 difference) 37-01, insoluble 0-68.— Dr. G. T. Prior: " On the Classifica- 

 tion of Meteorites." For purposes of the classification of meteorites 

 the significance is pointed out of the chemical composition of the, 

 nickel-iron and the magnesium silicates. In the case of meteoric 

 irons the structural features, as revealed by etching, are shown to 

 be closely related to the content of nickel. In meteoric stones the 

 proportion of magnesia to ferrous oxide in the magnesium silicates 

 varies directly with the proportion of iron to nickel in the nickel- 

 iron. On these principles the four classes of meteorites, viz. irons, 

 stony-irons, chondrites, and achondrites, can be divided into inter- 

 related groups. The three groups of chondrites are distinguished 

 as enstatite-chondrites, bronzite-chondrites, and hypersthene- 

 chondrites, according to the chemical composition of the pyroxene. 

 The achondrites are divided into corresponding groups of enstatite- 

 achondrites, bronzite (-augite) - achondrites, and hypersthene- 

 achondrites, while a fourth group is added richer in lime (and mostly 

 also in alumina) than the chondrites. To avoid confusion owing to 

 Brezina's misuse of the term chladnite, the enstatite-achondrites, 

 comprising Aubres, Bustee, and Bishopville, are called Aubrites, 

 while for the hypersthene-achondrites (Shalka, etc.) a reversion is 

 made to Tschermak's original name of diogenite. — A. F. Hallimond : 

 " On Torbernite." In continuation of the author's previous work 

 a series of weighings were ma,de on Gunnislake material held over 

 various concentrations of sulphuric acid. Dehydration did not 

 occur at the pressure required, and only took place slowly over strong 

 acid in a period of many months. It is clear that this mineral 

 cannot be identical with ordinary torbernite. The refractive index 

 agrees with that found for an abnormal torbernite by N. L. Bowen. 

 Normal torbernite has the density 3-22 and mean index 1-585, 

 while for artificial metatorbernite and for the Gunnislake mineral 

 the density is 3-68 and the index 1-624. An approximate reading 

 yielded for Gunnislake crystals c : a = 2-28 : 1. The basal planes 

 of the two forms are of the same dimension and the volume change 

 due to the addition of 4H2O is borne by an increase in the vertical 

 axis. The density of the water of crystallization is 1-2, a value 

 common in hydrated salts, while the refractive power is equal to 

 that for liquid water. 



