Miscellanies. 417 



2. Singular crystals of Lead from Rossie, N. Y. — These crystals, 

 figured in Alger's and Dana's Mineralogy, have received the following 

 explanation by Mr. J. E. Teschemacher, (p. 500, Vol. IV, Bost. Jour. 

 Nat. Hist.) While crystallizing from the melted state, " the uncooled 

 liquid central portion pressed by the contraction of the cooling exterior, 

 oozes out from the middle of the plane and spreads in a thin liquid 

 plate over part of the surface, taking nearly the form of the plane ; con- 

 traction still continuing, a succession of thin plates ooze out, each of 

 course spreading somewhat short of its predecessor, but retaining the 

 same form." He illustrates it by remarking, that on examining with 

 a microscope the cooling of a globule of phosphate of lead, " the an- 

 gles of the planes appear to start out from the circumference, as the 



outer surface of the globule cools and the planes to flatten into their 



symmetrical shape." 



But these crystals of galena are cleavable to the very centre like 

 others of this mineral, showing that instead of this oozing from the 

 interior, they were formed throughout by successively applied laminae. 

 The peculiar distorted form appears to be attributable to their confine- 

 ment in the limestone, already partially hardened around them when 

 they were crystallizing, and to the peculiar laws of crystallization by 

 which planes are added to the surfaces of a primary— this intercepted 

 mode of modification being by no means uncommon. 



3. Dipyre.— (Extract from an article by M. Achille Delesse, Comp- 

 tes Rendus, 1844, May 20, p. 944.)— This name was given by Laumont 

 and Charpentier to a mineral from the vicinity of Mauleon in the Lower 



Pyrenees, but has since been referred to the species Scapolite. It occurs 



in square or regular 8-sided prisms, cleavable parallel with the lateral faces 

 and the diagonal. The crystals are usually transparent and vitreous, 

 though sometimes partially decomposed and opaque. It occurs with talc 

 or chlorite, or an unctuous argillite. The mineral was imperfectly analy- 

 zed by Vauquelin. I obtained for the mean of four analyses, silica 55 5, 

 alumina 24.8, lime 96, soda 94, potash 07. From the large proportion 

 of alkali, the mineral appears to be allied to the feldspars. Von Kobell, 

 some time since, referred it to Labradorite, but the system of crystalliza- 

 tion is not the same; the specific gravity of Labradorite is 2714, and 

 that of dipyre 2646; moreover the composition, although similar, is still 

 essentially different, and appears to show that it is distinct also from Sca- 

 polite. The formula it affords is the following, 





••• •"• 



2(Ca,Na,K)Si-f3AlSi. 

 Before the blowpipe dipyre loses its transparency and fuses with a slight 

 effervescence, yielding a white blebby glass. Melts easily with salt of 

 phosphorus, and the pearl formed contains a floating skeleton of silica. 



