264 Mr W. Haidinger on Isopyre. 



were given to Mr Allan by Mr Joseph Carne of Penzance, 

 whose collection of minerals is particularly rich in the products 

 of the western districts of Cornwall. The west of Cornwall 

 is certainly the native country of the isopyre, but I am 

 unable at present more accurately to indicate its locality, as I 

 then considered the substance actually to be, what it was called, 

 black opal, and, as such, much less interesting than it proved on 

 more attentive examination, and omitted to take a note of the 

 exact locality. 



The resemblance of the isopyre to obsidian, or to what might 

 be supposed to be the appearance of opal, when of a black co- 

 lour, is very considerable ; only the lustre of isopyre is less 

 bright and glassy than that of obsidian. It is also very much 

 like certain varieties of iron slag, and in fact it would be diffi- 

 cult to suspect the mineral not to be a product of the same kind 

 of fusion which we are capable of producing in our own furna- 

 ces, if it were not associated with crystals of quartz, or did not 

 contain, as in one of Mr Allan's specimens, small imbedded crys- 

 tals of tin-ore and of tourmaline. In allusion to this appear- 

 ance, and also on account of the perfect similarity of a globule 

 melted before the blowpipe, with the fragment employed in the 

 experiment, I propose the trivial name of Isopyre, for designa- 

 ting the mineral, from la-cq equal,, and tcv^ fire. The similarity 

 of properties is even preserved in regard to magnetism, the glo- 

 bule obtained by exposing a fragment of the mineral to the blast 

 of the blowpipe being magnetic, as well as the fragment itself, 

 and even in a higher degree. 



From the description given * of the Tachylite of Breithaupt, 

 this mineral should much resemble the isopyre. Its specific 

 gravity is much lower, being only 2.5...S.54, so as to preclude 

 the possibility of their belonging to the same species. It occurs 

 in basalt and wacke at Saesebuehl, near Goettingen, likewise on- 

 ly massive. 



• Leonhard, 2d edit. p. 781. 



