232 Intelligeme and Miscellaneous Articles, 



mineral, probably albite, on which were several extremely minute 

 but beautiful octahedral crystals, of a deep orange to a wine -yellow 

 colour, the smallest transparent, the largest translucent on edges. 



At first I considered this a new mineral, until, on comparing it 

 with the account of pyrrhite, in Jameson's Edinburgh Journal, vol. 

 xxix., the resemblance struck me. I therefore sacrificed these cry- 

 stals to the blowpipe ; they gave the following indications : — 



The minutest transparent crystals changed immediately, in the 

 reducing flame, to a deep, dull indigo blue, perfectly distinct ; the 

 edges then rounded, and, after considerable exposure, fused without 

 intumescence ; on the application of borax, the fusion was immediate, 

 and a small, transparent, light brown bead remained. The largest 

 crystal was then exposed to the outer flame ; it became opake, of a 

 light gray colour ; before the reducing flame it changed apparently 

 to black ; but the blue colour is clearly seen, in a strong light, on 

 the solid angles. Of this crystal the edges alone could be rounded 

 by long exposure. 



The hardness is about equal to felspar, and the form is that of the 

 regular octahedron. Although this form is unknown among titanic 

 minerals, the experiments of Kersten lead me to suppose that it be- 

 longs to this family. 



Bucholzite and Xenolite. 

 In April 1843, 1 read a paper before this Society, which was pub- 

 lished among their Proceedings, in which I asserted the identity of 

 these two minerals. This has been confirmed by Rammelsberg, in 

 his Supplement, published July 1843, from a consideration of the 

 similarit}'^ of their chemical constituents. This question may there- 

 fore be considered as settled; but it is not probable that Rammels- 

 berg had seen the paper alluded to above. 



On the singular Crystals of Galena, figured in Alger's and in Dana's 



Mineralogy. 



A good explanation of the formation of these singular crystals may 

 be given as follows : — It is well known that a liquid globule of phos- 

 phate of lead, on cooling, from the action of the blowpipe, takes a 

 polyhedral form, generally that of a rhombic or pentagonal dodeca- 

 hedron. 



A microscopic examination of this cooling process shows that, as 

 the outer surface of the globule cools, the angles of the planes appear 

 to start out from the circumference, the planes to flatten into their 

 symmetrical shape ; 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 sur- 

 face, taking nearly the form of the plane ; contraction still continu- 

 ing, a succession of thin plates ooze out, each of course spreading 

 somewhat short of its predecessor, but retaining the same form. 

 This is probably the mode of the formation of these crystals of Ga- 

 lena, all of which bear the appearance of having undergone fusion. 

 On many crystals of fluor spar from England, successive plates of 

 this kind may be observed ; many of them, however, do not take 



