388 S. L. Penfield — Broohite from Magnet Cove, Arlc. 



mentioned forms and usually appears with very small faces. 

 One hand specimen of a very much decomposed siliceous rock 

 contained a great number of small lustrous crystals about < 2 !nm 

 in diameter, which show a very large development of t, fig. 

 3, but I have seen no large crystals with this habit. The 

 macropinacoid a appears very frequently, but seldom largely 

 developed. 



The crystal which first attracted my attention is about 

 Y mm in its greatest diameter with very lustrous faces and sym- 

 metrical development; it is only a fragment. It shows all of 

 the forms mentioned above with the addition of £, which bevels 

 the macrodiagonal pole edge of z. / is a rare pyramid in this 



species, and was first identified by von Leuchtenberg* on crys- 

 tals from the Urals. The planes are arranged as in fig. 4. It 

 will be noticed that the prominent pyramid is here z, while e is 

 very subordinate. I have been able to find no duplicate of 

 this crystal. Except the large rough crystals which are wholly 

 changed into rutile, and which have the habit shown in fig. 4, 

 only with more prominent prismatic development; all that I 

 have seen show the pyramid e largely developed. The two 

 pyramids z and e might be mistaken for one another were it 

 not for the prism m which serves for orientation. 



The angles which were measured and served for the identifi- 

 cation of the faces (on crystal shown in fig. 4) are given in the 



* Materialmen zur Mineralogie Russlands, vi, 204. 



