Mineralogy. 387 



Sulphur, 25-910 



Arsenic, 28-556 



Lead, 44-564 



Silver, 0424 



Iron, 0-448 



99-902 

 This analysis does not lead to any simple formula, but the author infers 

 that the mineral is a mixture of two substances having the formulae 

 PbS -f- AsS 3 and 2PbS -f- As S 3 in the proportion of about 3 to 1. The 

 latter is obviously the mineral analyzed by Damour ; and as the author 

 has retained the name of Dufrenoysite to the mineral crystallizing in the 

 regular system, he proposes to call this substance Scleroclase, while 

 PbS + AsS 3 , which, however, has not yet been obtained in the pure state, 

 he calls Arsenomelan. The results of several other analyses show that 

 these minerals may occur mixed in variable proportions although the 

 crystalline form remains unchanged. 



Oxygenized Minerals. — Among these occur magnetic iron ore, rutile, 

 bitter spar, spathic iron ore, rock crystal, talc mica, and white and aspa- 

 ragus-green tourmaline. There are also two other substances of con- 

 siderable interest. One is a fine right-prismatic crystal ; hardness 3*5, 

 specific gravity 3*977 ; it is a sulphate of baryta, containing 9 per cent, 

 of sulphate of strontian. The other mineral is pure white, and some- 

 times perfectly transparent ; hardness between felspar and quartz, speci- 

 fic gravity 2*805. Its crystals belong to the oblique prismatic system, 

 and closely resemble those of adularia. The ratio of the axes is 

 a : b : c =■: 1* : 0-65765 : 0*54116, and the inclination of z on y = 64° 16' 

 8". Its analysis gave — 



Silica, 24*127 



Alumina, . . . . 49*929 



Lime, 1*570 



Magnesia, .... 0*420 



Soda, 5*742 



Baryta, 14*403 



Sulphuric acid, . . 2*702 



Water, 0*650 



99*543 



From this he calculates the excessively complicated formula 5(3A1 3 

 Si 3 ) • 3(2110 Si 3 ) = Ba OS 3 , and gives it the name of Thyalophan. 

 It is clear that this formula must at present be considered as very ques- 

 tionable. 



The paper concludes with some theoretical considerations as to the 

 mode in which dolomite has been produced. — (Poggendorff's Annalen, 

 vol. xciv. p. 115). 



Remarkable Brazilian Diamond. — The largest and finest diamond 

 which has as yet been found in Brazil, has recently been imported into 

 Paris, and has received the name of the " Star of the South." In its 

 rough state it weighs 807'02 grains or 254^ carats. When cut it will be 

 reduced to about 127 carats, and will therefore exceed the Koh-i-noor in 

 size. Independently of its magnitude it possesses much scientific interest 

 from the regularity of its crystalline forms, and the indications it affords 

 of the mode in which the diamond occurs. The general form of the ' ' Star 

 of the South" is a rhomboidal dodecahedron, having each of its faces 

 bevelled by a face set on very obliquely, so that it has in all 24 faces. On 

 one of its faces there is a pretty deep cavity obviously produced by an 

 octahedral crystal which has been implanted in it. The interior of this 

 cavity when examined with a lens shows octahedral striae, and it cannot 



