48 Mr Haidinger on the Crystalline Forms 



posed in reniform coats. The specific gravity of those parts, 

 which possess a rather stronger lustre, and a conchoidal frac- 

 ture, is = 4.004, while the specific gravity of those without 

 lustre, and an uneven fracture, was found to be =: 4.079- 



IV. — Brachytypous Manganese Ore. 



Fundamental form. Isosceles four-sided pyramid. P — 

 10SF 53' 108° 3&. Fig. 15. 



a = v /l .94. 



Simple forms. P — co (o) ; P(P), Wunsiedel, Bayreuth ; 

 P+2 (s) = 96 # 33', 140° 30', Fig. 16., Elgersburg, Thurin- 

 gia; (P+lf(z) = 144° 4', 128° If, 154° W. 



Char, of comb, pyramidal. 



Combinations. 1. P — od . P. Fig. 17., Wunsiedel. 



2. P. P+2. Fig. 18., Elgersburg. 



3. P. (P+l) 3 . Fig. 19., St Marcel, Piedmont. 



4. P — oo. P. P+2. Fig. 20., Wunsiedel. 



Cleavage, very distinct in the direction of the faces of P ; 

 entire forms of cleavage may be obtained from larger indivi- 

 duals. Fracture uneven. Surface, P — co, possessing less 

 lustre than P, but even, and sometimes faintly streaked pa- 

 rallel to the edges of combination with P ; P often a little 

 rounded ; P + go uneven, rough and horizontally streaked ; 

 (P+ l) 3 smooth and even. 



Lustre imperfect metallic. Colour dark brownish-black. 

 Streak of the same colour. 



Brittle. Hardness = 6.0 . . . 6.5. Sp. Gr. == 4.818, large 

 cleavable individuals from Elgersburg. 



Compound Varieties. Massive : composition granular, in- 

 dividuals strongly coherent. 



Observations. 

 The first variety of the species of brachytypous Manga- 

 nese-ore which I had the good fortune to examine, was 

 brought by Dr Turner from Germany, the ticket bearing the 

 locality of Elgersburg. Being struck with the facility with 

 which this mineral yields to cleavage in the direction of the 

 faces of a four-sided pyramid, and supposing it to belong to 



l 



