of the red oxyd of Copper and arseniated Iron. 33 



of an arrangement that may not be allowed strictly to come within 

 the meaning of the term macle^ in the sense in which it is used by 

 Rome de Tlsle, being simply two crystals of the last variety, uniting 

 by one of the four hexagonal faces of each crystal, so as to form in 

 appearance but a single crystal. I possess also another, in which 

 two crystals of the si^cceeding variety are in like manner attached. 



Fig. 12 is a highly interesting variety of the primitive crystal, as 

 It forms the passage of it, as fig. 13 will shew, into the acute rhom- 

 boid, fig. 15, of which fig. 14 is the intermediary stage. This 

 rhomboid, I have not, from the minuteness of the crystals, which, 

 though numerous, exceed not in size the extremity of the smallest 

 pin, been able to submit to the goniometer. This form also exists in 

 the Spinelle ruby and in the diamond ; which, as well as the red 

 oxyd of copper, have for their primitive form, the regular octohedron, 

 and give an acute rhomboid of 60 and 120d. 



THE FIRST MODIFICATION. 



This modification consists in a decrease on the six solid angles of 

 the primitive crystal, so that each is replaced by an equilateral quad- 

 rangular plane, perpendicular to the axis that passes through the 

 angle, and forms the passage of the octohedron into the cube. The 

 angle caused by the meeting of the faces P and 1, Fig. 16, is, 

 according to Haiiy, 125% 15', 52". Fig. 21 shews the direction of 

 the laminse of the cube. Fig. 25 may rather be considered an acci- 

 dental circumstance, than as forming an important part of this series. 

 That the triangular face formed by the decrease of crystalline laminse 

 on the solid angle of the cube (fig. 24.) corresponds with the face 

 P of the primitive crystal will be obvious. I could not therefore 

 hesitate to delineate this interesting combination, of which several 

 instances occurred on the same specimen. Fig. 29 represents the 



£ 



