irf Manganese Ores. -A9 



the species of the pyramidal manganese-ore of Mohs, I re- 

 quested Dr Turner's permission to extract the form of cleav- 

 age from it, but was much surprised when I could not dis- 

 cover the single cleavage perpendicular to the axis, which is 

 so very distinct in that mineral, and has been likewise indicat- 

 ed by Messrs Brooke and Phillips. Though the mineral 

 cleaves very readily, yet its great hardness, being superior to 

 that of feldspar, and a strong connection among the particles, 

 render it extremely difficult to obtain the faces smooth and 

 plain enough to reflect a good image even of a single very 

 luminous point. I was, therefore, led to suppose, by several 

 approximate measurements, that the regular octahedron 

 should be considered as the fundamental form of the species. 

 In some of the cavities of the same specimen there were, how- 

 ever, crystals in the form of acute four-sided pyramids, simi- 

 lar to Fig. 1 6, which did not agree with the symmetry of tes- 

 sular forms. They were rough, and possessed of little lustre, 

 so that they afforded only indistinct measurements of about 

 140° for the base of the pyramid. Certain varieties from 

 Wunsiedel in Bayreuth, in the cabinet of Mr Allan, engaged 

 in heavy-spar, and associated with prismatoidal manganese- 

 ore in very delicate columnar composition, possess the form of 

 Figs. 15, 17, and 20. The two first of these I also observed 

 in a specimen in the collection of Mr Ferguson of Raith, hav- 

 ing the following ticket by Mr Heuland : " Hydrous-oxide of 

 manganese, in the form of an octahedron, with a square basis. 

 Thuringia — is extinct." As Haiiy's works contain the pyra- 

 midal manganese-ore of Mohs, under the denomination of 

 Manganese oxide hydrate,* this specimen is probably intend- 

 ed for a variety of that species, which, however, is very inac- 

 curately described by Haiiy, who united under one head the 

 physical properties of one species with the physical and the 

 chemical properties of two or three others to form a general 

 description, to which no object in nature corresponds. I had 

 long ago observed crystals of the form Fig. 19, engaged in a 

 specimen of the epidote manganestfere of Haiiy, in the cabi- 

 net of Mr Allan, but which I believed likewise to be a variety 



• TraiU-, 2(lc Ed. t. iv. p. 264. 

 VOL. IV. NO. I. JAN. 1826. , D 



