﻿176 Shepard's Treatise on Mineralogy. 



3. 



Identity of Fibrolite and Sillimanite. — I have been led to 

 regard these substances as identical, because in addition to an 

 agreement in hardness and gravity, I had found nothing incon- 

 sistent in their crystalline structure. For although no regular 

 form of the first mentioned variety has been found, I have still 

 observed that when a fresh longitudinal fracture of the Carnatic 

 mineral is made, that in a strong light, (aided by a single lens,) 

 there come into view, the same brilliant, micaceous cleavages in 

 the slender individuals composing the mass, as happens in the 

 ordinary Bucholzite varieties of Sillimanite. 



4. Lederite.—Mr . J. D. Dana remarks in his Mineralogy, (2d 

 edit., p. 422,) that this mineral " is identical in crystallographic 

 as well as other characters, with common sphene," an opinion 

 which is also expressed in the last number of this Journal, p. 350, 

 and again previously, (Vol. xlvi, p. 36.) The mineral in ques- 

 tion was removed by me from sphene, on account of its apparent 

 inconsistency in cleavage, with the latter, as well as from its dis- 

 agreement in angular values with any known crystals of sphene. 

 In my original paper (Vol. xxxix, p. 357) I suggested that should 

 these discrepancies continue to be unaccounted for, and the min- 

 eral be allowed a specific character of its own, that I should be- 

 speak for it the name of Lederite. I object to the above method 

 of restoring this substance to its former place, since the difficulty 

 of cleavage still remains where I found it, and that of angles does 

 not appear to me to be satisfactorily smoothed away, by saying 

 that it differs but 1° 22' in one angle, and 1° 36' in another, from 

 a figure of sphene contained in Mohs' Mineralogy. Besides 

 it is not true, as asserted in one of the above notices, that my 

 angles were obtained with the common goniometer. I am, 

 however, far from denying that the two substances may yet be 

 shown to coalesce; it is only here maintained, that the uncertainty 

 hanging over the subject is where it was first left. 



*>• Goshenite.—A crystal of this substance, lately obtained by 

 me at the locality, affords a triangular plane on one of the angles, 

 whose inclinations to the adjoining prismatic and terminal faces, 

 aie so near to the values of the corresponding angles in beryl, 

 as to remove all probability that these minerals can be shown to 

 be crystaUographically distinct. 



Ii . * Iicrohte.— The dimensions of the controversy to which this 



mineral has already given rise, seem half entitled to place 



