Oti the Hoiighite of Pro/.lShepard. 365 



* 



In another specimen, in Dr. Hough's collection, there were the 

 summits and faces of several perfect octahedrons. The solid 

 angles had the hardness and lustre of spinel ; but portions of the 

 faces were destitute of lustre, or only glimmering, from dissem- 

 inated particles of spinel, and were easily scratched by the knife. 

 This specimen consists of three almost perfect crystals, each 

 about f ths of an inch in diameter, besides three of smaller size. 

 The whole was imbedded in serpentine and dolomite. These 

 crystals are formed of mixed spinel and Houghite. The spinel 

 seems to predominate on the edges and solid angles ; but some of 

 the well defined edges yield to the knife. When a crystal is held 

 so as to reflect light to the eye, it is very easy to distinguish the 

 two minerals. It is seen that they are irregularly disposed, and 

 yet follow certain lines of cleavage which are not parallel, often 

 curved and generally unsymmetrical with the figure of the crys- 

 fal They seem free from the milk-white color which is observed 

 m the amorphous masses, and no doubt contain the true specific 

 Houghite. In another large octahedral crystal of regular form, 

 the exterior is whitened and altered to the depth of half a line. 



Many interesting facts and speculations have occurred to me in 

 relation to the origin of this mineral. Its association with spinel 

 as Well as the similarity to that mineral in the bases in its com- 

 position, are facts of great interest. It might appear that they 

 ^ere simultaneously formed, since they occur together, in such 

 intimate mixture, and yet are so well defined. Possibly when 

 the spinel has predominated to a certain extent, or been placed 

 in otherwise favorable conditions, its crystallizing force, in causing 

 It to assume its own peculiar form, has impressed that form on the 

 Houghite, analogous to what has occurred in the Fontainbleau 

 limestone. But there are objections to this view, since spinel, ac- 

 cording to the experiments of Ebelmen, is of purely igneous ori- 

 gin, and the circumstances attending its formation are incompati- 

 ble, as far as we know, with the simultaneous production of a 

 hydrous mineral, 



[Note on ike probable Identity of Houghite and Volknerite. 

 Mr. Johnson has observ^ed that we cannot obtain from the analyses 

 a satisfactoiy view of the composition of the mineral, owing to 

 fne uncertain results. The analyses are still sufficient lo author- 

 ize the suggestion that Houghite', when pure and free from car- 

 ^nic acid, may be identical with the Volknerite of Hermann * 

 Hermann obtainedlfor the Volknerite, 



Xl rt-CS, '^s S8-59 fl 43-'76 



This gave Hermann for the oxygen of the alumina and mag- 

 nesia the ratio 1 : 2, [more exactly 1 : 1'84] while the analyses of 



* Journ. I prakt. Chem., xl, 11, and Dana's Mineralogy, 3 J 

 Second Series, VoL XII, No. 36.— Nov., 1851. 47 



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