Examination of Hyalosiderite, a neiv Mineral. 183 



Fracture small conchoidal ; external lustre metallic, of the 

 fracture vitreous; hardness, in newly exposed crystals, be- 

 tween that of felspar and that of apatite ; cleavage at right 

 angles to the axis of the octahedron AA' (fig. 9), not very 

 perceptible. 



Transparent on the thin edges, or in small splinters, with 

 a hyacinth red colour passing into a wine-yellow ; the streak 

 of a cinnamon colour. Specific gravity 2*875 ; temp. 70'7 F. 



Single crystals are sometimes attracted by the magnet ; but 

 always after they have been made slightly red hot, by which 

 they are rendered black. 



Before the blow-pipe they immediately become black and 

 melt into a globule, which is attracted by the magnet. 



With borax they are readily and completely reduced to a 

 transparent glass, which, while hot, has a yellowish-green co- 

 lour, that almost entirely disappears on cooling if but little of 

 the mineral has been employed; but if the borax be saturated 

 with it, it becomes black and opake. They are dissolved by 

 salt of phosphorus into a clear greenish glass", leaving a skeleton 

 of sdica behind, and the glass after cooling becomes colourless. 



If the boracic glass, containing a small portion of the mi- 

 neral, be cautiously treated with tin, the globule, after it has 

 become quite cold, exhibits a slight but determined beautiful 

 green colour. 



§ 4. 

 From the nature of the forms above enumerated we may 

 assume, that the system of crystallization of this mineral is a 

 tnmetric one *. The planes d and d, presenting themselves 

 most frequently, and which form the rectangular octahedron, 

 appear then as bounding planes, which truncate rectangularly 

 the edges of the base of the ground form ; the planes a as the 

 horizontal, and the planes P as the primary planes, since the 

 edges, which those planes form with the planes d! and d, are in 

 parallelism with each other. 



§ 5. 

 The primary planes are too small for the measurement of 

 their mutual inclination. The inclination of the planes d and 

 d' may be determined most exactly, although, on account of 

 the smallness of the crystals, even these measurements remain 

 imperfect. The inclination of d on d! was determined to be 

 141°, and the inclination of d' on a amounted to rather more 

 than 130°. Now if these measurements are taken as the basis 

 for determining the mathematical character of the primary 



• Hausmann Unfert. ub. d. Form. d. Icbl. Nat. i. p. 417. 



form, 



