G. W. McKee — Prismatic Crystals of Hematite. 241 



Art. XXII. 



■ Prismatic Crystals of Hematite; by G-. W. 

 McKee. 



The common forms for hematite crystals are rhombohedra 

 and scalenohedra. Prismatic faces are seldom well developed. 

 The basal pinacoid is still rarer. Specimens of well crystal- 

 lized hematite showing crystals of an unusual habit were 

 obtained recently from Dr. A. E. Foote, Philadelphia. These 

 specimens are reported to be from Guanajuato, Mexico. The 

 crystals, which are very small, seldom more than a millimeter 

 in diameter, are well formed and possess a bright metallic 

 lustre such as is characteristic of the specimens from Elba. 

 They occur spread in a layer over the surface of a much 

 decomposed rock, which is probably a rhyolite. 



A few of the best crystals were selected for measurement on 

 a Goldschmidt two-circle reflecting goniometer. Some of 



them showed combinations of the prism { 1010 } and base 

 {0001 1, while others presented in addition to these forms 

 several pyramids of the second order. In all cases, however, 

 the most prominent forms were the prism {1010} and the 

 base { 0001 } . These faces ordinarily play a very subordinate 

 part in the crystallization of hematite and by their prominence 

 here we obtain a distinct prismatic crystal habit hitherto rarely 

 recorded for hematite. The results of the measurements on 

 two crystals are given in detail and along with them, for pur- 

 poses of comparison, the calculated results for the symbols 

 deduced. If we consider the pyramids as of the second order 

 then the prism becomes the prism of the first order. All the 

 forms observed here are already well known, the complete list 

 being as follows:— {0001 }, {1010}, {1128}, {1122}, {2241}. 



