328 Mr Haidinger on. Davyne, 



compliment to Prince Christian had been paid by a mineralo- 

 gist better versed in the literature of his science. 



Humboldtilite, Davyne, Cavohnite, Biotine have been de- 

 scribed as new species ; I select Davyne for the subject of the 

 present communication, as I have lately had an opportunity of 

 examining several of its properties in specimens of Mr Allan's 

 cabinet. The following description is drawn up from them, to 

 which are added the varieties observed by Messrs Monticelli 

 and Covelliin a much more comprehensive series of specimens. 



Form rhombohedral. Crystals similar Fig. 5. Combina- 

 tion. R — CO (P). P (r). R-}- QD (s). P -f o^CM). The 

 faces r sufficiently enlarged produce an isosceles six-sided 

 pyramid, with terminal edges of 154° 46', and lateral edges of 

 51° 47', nearly, as deduced from the admeasurement of the 

 latter. The fundamental form, from which this pyramid de- 

 rives, is a rhombohedron of 112° 16', whose axis is = ^1.59- 



Cleavage highly perfect, parallel to the faces M, or P -}- oo, 

 cross fracture conchoidal. 



High degrees of lustre upon the faces of cleavage, which by 

 the numerous parallel fissures to them often assume a pearly 

 aspect. The surface of the faces r is often a little rough, 

 though perfectly even. Colour white. Transparency consi- 

 derable. 



Brittle. Hardness = 5.0... 5.5, a httle above apatite. Spe- 

 cific gravity nearly 2.4. 



In the specimens which I examined, the Davyne was associa- 

 ted with brown dodecahedral garnet. They had been sent to Mr 

 Allan by Lord Compton. Beside the variety represented in 

 th6 figure, Davyne is described by Messrs Monticelli and 

 Covelli as occurring in the combinations of the six-sided prism 

 M, consisting of P, and with r and s separately, of different 

 brownish tints, and various degrees of translucency. They 

 state the specific gravity at 2.25. I am confident that the one 

 of 2.4 given above approaches nearer truth, though I could 

 not arrive at a result entirely to be depended on, from having 

 too small a quantity of the material. 



In contrasting the properties of Davyne with those of n&. 

 pheline, the specific gravity of the latter is quoted as high as 



