

216 Miscella nies. 



tals of this mineral from the same region, and infers from his investiga- 

 tions that the forms are distinct, although both belong to the dimetric 

 system. The crystals of anatase are rarely octa- 

 hedrons; the annexed figure is one of the forms. 

 They differ from rutile in cleavage, and upwards 

 of '3 per cent, in specific gravity. If an instance 

 of dimorphism, as it appears, it is remarkable that 

 both forms belong to the same system of crystalli- 

 zation. (Ann. Ch. Ph. 3d ser., April 1844, pp. 414 and 418.) 



5. Pennine. — According to Marignac and Descloiseaux, the primary 

 of this mineral is an acute rhombohedron of 63° 15'. This form is some- 

 times presented by minute crystals, but the larger are usually flat tables, 

 arising from a truncation of the extremities. Specific gravity 2'653. An 

 analysis of specimens from the valley of Zermatt afforded Silica 33*36, 

 alumina 13 24, chromic acid 0*20, peroxyd of iron 5*93, magnesia 34*21, 

 water 1280, from which Marignac and Descloiseaux deduce the formula 



» • < 



2A1, Mg+5Si, Mg 2 H 2 . (Ibid. p. 427.) The above formula, omitting 

 one atom of water, which the calculation according to the above gives in 



* • f • * t 



excess, may be written 2AlSi-f 3Mg 3 Si-f 3MgH 3 , which, except in the 

 proportions of the silicates, is similar to Varrentrapp's formula for chlo- 

 rite. — D. 



6. Talc. — This mineral from Chamouni, analyzed by Marignac and 



•♦ • 



]'98, water 004=100, from which they obtain the formula 

 (Ibid.) 



i 



7. Dioptase.— Damour has obtained for the formula of Dioptase, 



Cu 3 Si 2 H 3 . His analysis gave Silica 3647, oxyd of copper 5010, wa- 

 ter 1140. (Ibid, p. 485.) 



8. Beaumontitc. — This mineral from the vicinity of Baltimore, MAi 

 has been analyzed by M. A. Delesse with the following results I Silica 



and loss 06, water 134 ; from which he deduces the formula RSi 2 + A1 



••• 



Si 3 -f-5H. In a closed tube it whitens and intumesces, and a plat" 13 

 wire affords a white opaline pearl. With salt of phosphorus it forms ea- 

 sily a glass with a skeleton of silica. Specific gravity=2'25. (Ann. *> 

 Ch. et de Phys. 3e ser., ix, 385, 1843.) Notwithstanding the above re- 

 sults, Beaumontite is probably nothing but Heulandite. The primary « 

 not a square prism, as given by Levy, which fact is evident from the dis- 

 similar lustre on the faces assumed as the prismatic faces by l**h aD 



