500 Mineralogical Notices. 



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 grey 

 color ; before the reducing flame, it changed apparently to 

 black ; but the blue color 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 octohedron. Although this form is unknown 

 among titanic minerals, the experiments of Kersten lead me 

 to suppose that it belongs to this family. 



BUCHOLZITE and XENOLITE. 



In April, 1S43, I read a paper before this Society, which 

 was published 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 similarity of their chemical con- 

 stituents. This question may therefore be considered as 

 settled ; but it is not probable that Rammelsberg 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 phosphate of lead, on cooling, from the ac- 

 tion of the blowpipe, takes a polyhedral form, generally that 

 of a rhombic or pentagonal dodecahedron. 



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 surface, taking nearly 

 the form of the plane ; contraction still continuing, a succes- 



