ORDEttX. PYRAMIDAL COPPER-PYRITES. 471 



Compound Varieties. Twin-crystals : face of 

 composition parallel, axis of revolution perpendicu- 

 lar to a face of P, similar to the composition of the 

 octahedron. Fig. 156; 2. Face of composition per- 

 pendicular, axis of revolution parallel to a terminal 

 edge of P -f 1. This law is complementary to the 

 preceding one ; 3. Face of composition perpendi- 

 cular, axis of revolution parallel to one of the ter- 

 minal edges of P. These three kinds of regular 

 composition are not only often repeated in parallel 

 layers, and contiguous to the different homologous 

 parts of the crystals, but they are even found to 

 take place at the same time. Globular, reniform, 

 botryoidal, stalactitic, and other imitative shapes : 

 surface generally rough, sometimes also smooth, 

 composition impalpable, fracture flat conchoidal. 

 Massive : composition granular, of various sizes of 

 individuals, often impalpable, and commonly strong- 

 ly coherent, fracture uneven or flat conchoidal. 



OBSERVATIONS. 



1. Pyramidal Copper-pyrites has been found to contain 

 Copper 30-20 30-50 41-00 32-00 34-40 33-12. 

 Iron 32*30 33-00 17*00 34-00 30-47 30-00. 



Sulphur 37-00 35-00 45-CO 33-00 33-87 3TJ-52. 

 Silica 0-00 0-00 0-00 0-00 0-27 0-39. 



GUENIVEAU. L.AMPAD. BREITH. H. ROSE. 



Upon charcoal ft becomes black before the blowpipe, and 

 red on cooling. It melts into a globule, which becomes 

 magnetic if kept in the blast for some time. With borax 

 it yields a globule of copper. It is partly soluble in dilute 

 nitric acid ; the solution is green, and the undissolved park 

 consists of sulphur. 



