Scientific Intelligence — Mineralogy. 193 



ffraphicform is similar to that of the zircon, but not identical. It 

 presents no distinct cleavage, and the fracture is small conchoidal. 

 The hardness is that of felspar, and it is, of course, easily scratched 

 by zircon. The specific gravity = 3 '903, while that of zircon 

 = 4'4 to 4*6. Colour, bluish-white ; but that of the surface of 

 the crystals is generally rendered brownish, reddish, yellowish, or 

 blackish, by a thin coating of foreign substances. The lustre of the 

 crystalline faces is vitreous, but feebler than in zircon ; and that of 

 the fractured surface is resinous. In small fragments it is translu- 

 cent, with a yellowish-white colour. The streak is colourless. The 

 following is the result of a quantitative analysis : — 



Silica, 31-31 



Zirconia, 63"40 



Oxide of Iron, .... O'il 



Yttria, 0-34 



Lime, 0-39 



Magnesia, O'll 



Water, 3-03 



98-99 



It may be assumed that only the silica, zirconia, and perhap3 

 the water, are essential constituents of malakone. The substance 

 might thus be regarded as a zircon containing water, which, on being 

 heated, becomes converted into ordinary zircon, after losing its water, 

 and after exhibiting, to a certain extent, the pyrognomic property 

 presented in a greater degree by gadolinite and polykrase. Scheerer 

 considers it as probable, however, that the zirconia exists in malakone 

 in a different isomeric condition from the zirconia in zircon ; and that, 

 after being exposed to heat, it passes, with evolution of light, into the 

 same modification in which it is contained in zircon. Perhaps the 

 different isomeric condition of the zirconia is the only essential dif- 

 ference between zircon and malakone ; and this is rendered the more 

 probable, as, accoi-ding to Scheerer, no true hydrate is known which 

 contains so small a quantity of water as the malakone, and as there 

 are sevei-al other minerals in which a variable quantity of water dis- 

 appears on the application of heat. This is the case, for instance, 

 with some gadolinites, orthites, and elaolites. 



19, Sismondine, a New Mineral Species. — B. de Lom has found 

 a mineral at Saint Marcel, which has been described and analysed 

 by Delesse, and has i-eceivcd its name in honour of the mineralogist 

 Sismonda. It occurs in chlorite slate, and is associated with gar- 

 nets, titanic iron, and iron pyrites — colour, dark green; streaky 

 light greenish-grey ; scratches glass ; specific gravity = 3*565 ; 

 crystallographic form not yet determined ; distinct cleavage in one 

 direction; a considerable lustre ; fracture uneven. Its chemical 

 composition is the following : — 



VOL. XXXIX. NO. LXXVII. — JULY 1845. N 



