on the Crystalline Forms of the Haytorite. 41 



angles of 77° and 103°: the terminal plane declining from one 

 acute angle to the other. Some of the crystals foi'ming one 

 large group in my possession, are opaque, in others trans- 

 lucency exists ; and others again seem to have suffered a par- 

 tial decomposition, having the appearance of being carious 

 internally; but to what extent soever that appearance has 

 taken place, it is remarkable that the portion remaining of 

 the external plane, however small, is not deprived of its or- 

 dinary lustre, and often is even brilliant. 



Now if this apparent injury had been the real effect of de- 

 composition, we might expect that the agent producing it 

 would in the first place have acted externally, and thus have 

 deprived the external planes of their natural brilliancy ; and 

 this consideration again tempted the farther examination as 

 to whether there existed in the ci-ystals, thus partially hol- 

 low, any stalactitical appearance of chalcedonic matter : this 

 certainly does appear on a close examination by the help of 

 a glass ; a circumstance amounting almost to proof that the 

 crystals are in reality pseudomorphous, and that their sub- 

 stance is chalcedony : the smaller crystals were sometimes en- 

 veloped by it. 



But if pseudomorphous, the next question that arose was. 

 What was the oi-iginal substance of which the chalcedony had 

 taken the form : and being on this point completely at fault, 

 I showed a crystal to my friend H. J. Brooke, Esq. which he 

 submitted to the examination of Mr. Levy, who suggested 

 that the original substance might have been sphene; and 

 hence the suspicion already alluded to by Mr. Tripe. 



The primary form of sphene is likewise an oblique rhombic 

 prism ; but that which has hitherto been so considered, differs 

 greatly in measurement from the apparent primary form of 

 Haytorite. M. Levy will, perhaps, add his opinions on the 

 subject. 



Of the following figures, fig. 1. represents the ordinary 

 form of the large crystals, the planes r and c being always 

 striated, 5 always convex, d mostly rough and dull, k always 

 smooth, but dull. Fig. 2. represents a smallish crystal, with 

 bright planes except k, which is striated as in the figure. 

 Figs. 3. and 4. represent two transparent crystals scarcely 

 larger than flattened pins' heads, of which the planes are all 

 bright, except /". In the present uncertain origin of this mi- 

 neral, I have thought it better to give arbitrary signs to the 

 several planes, than to adopt the notation of Mr. Brooke. 



New Scries. Vol. I. No. I. Jan. Ib27. O Haytorite. 



