182 Dr. Walchner's Mineralogical and Chemical 



suits of it, together with the mineral, to my honoured teacher 

 M. Hausmann ; who acknowledged it to be a new mineral, 

 and was so good as to direct my attention to the analogy be- 

 tween it and crystallized iron slag. 



§ 2. 



Hvalosiderite occurs for the most part in crystals ; but like- 

 wise in small blunt-edged, friable, loosely coherent grains. 

 The crystalline forms hitherto observed in it are the following: 



(1.) The rectangular octahedron, having its terminal solid 

 angles replaced by tangent planes (fig. 1). 



This form varies, 



a.) By the different proportions of the terminal planes to 

 those of the octahedron. The former are sometimes so large 

 in proportion to the latter, that the crystallization acquires? the 

 appearance of a rectangular four-sided tablet bevelled on each 

 side (fig. 2). 



b.) By the elongation in either direction of the edges of 

 the base, which is sometimes so considerable, that the form 

 becomes prismatic (fig. 3). 



(2.) The same crystallization (1) with the greater edges 

 of the base replaced by tangent planes, those planes generally 

 small (fig. 4-). 



(3.) The same crystallization (1), with the greater edges 

 of the base replaced by two planes. The size of the new 

 planes varies in proportion to that of the others. They are 

 sometimes small (fig. 5), and sometimes so enlarged that the 

 planes of the octahedron on which they rest almost disappear 

 (fig. 6). • 



(4.) The same crystallization (1), with the solid angles of 

 the base replaced by two triangular planes, usually very small 

 (fig. 8). 



(5.) The same crystallization (1), with all the edges of the 

 base replaced by two planes (fig. 7). 



Twin crystals I have not met with. 



§ 3. 

 The crystals are very small, scarcely of the size of lentils ; 

 they appear when the amygdaloid has become disintegrated, 

 as they resist the action of the elements for a greater length 

 of time ; they are either attached to augite, or freely dissemi- 

 nated in the amygdaloid ; and are, for the most part, imper- 

 fectly formed. Their surface is smooth, and exhibits, in an 

 oblique light, sometimes a brass yellow, or a gold yellow co- 

 lour, sometimes the colour of tarnished steel ; which is owing to 

 a thin coat of perhydrate of iron, investing most of the crystals. 

 Their proper colour is reddish- or yellowish-brown. 



Fracture 



