88 Mr. Haidingcr on the Regular Composition 



Art. XIV. — On the Regular Composition of Crystallized Bo- 

 dies. By William Haidingkb, Esq. F. R. S. E. Com- 

 municated by the Author. — (Continued from Vol. I. p. 

 333.) 



Among those minerals of the rhombohedral system, which 

 present regular composition in directions inclined to the axis, 

 Calcareous spar is one, whose individuals assume a great num- 

 ber of different positions, and produce a variety of curious 

 and interesting phenomena ; not only from the position of 

 the individuals, but also from the mode in which their sub- 

 stance is extended in regard to the faces of composition. 



One of the rarer occurrences is represented Plate III. Fig. 1. 

 The form of the individuals is that of the rhombohedron, 

 R — 1, called equiaxe by Hauy. The axis of revolution is 

 parallel, the plaTtie of composition perpendicular to one of the 

 edges of this rhombohedron. Its crystallographic sign will 

 1 )e R — 1, f 11-2 : 11- l ~l. The rhombohedron in this variety 

 is occasionally combined with the faces of R + <x ; I found 

 it in the Ludewig vein in the mine of Beschertgluck, near 

 Freiberg. 



More frequently the regular composition is parallel to one 

 of the faces of R, the rhombohedron of 105° 5', which is the 

 fundamental form of the species. One of the most simple va- 

 rieties is that of Fig. 2, a group from the Hartz, in the col- 

 lection of the Mining Academy at Freiberg. Its sign is 

 R — or. R-r-cc, fy}- Thus, likewise, Fig. 3. is compo- 

 sed; the form of the simple individuals, however, is R — 1. 

 R + gd. This variety is from the Himmelsfurst mine, near 

 Freiberg. If the prism is long in comparison with the diame- 

 ter of the crystals, the compound group takes a geniculated 

 appearance, not uncommon among the claviform crystals from 

 Braunsdorf near Freiberg, of which Fig. 4. is a representa- 

 tion. I have seen a specimen from the same locality, in the 

 possession of Mr. Breithaupt, in which the substance of the 

 two individuals was continued beyond the face of composition, 

 and produced the cruciform appearance of Fig. 5, designated 



