8 
ON THE CRYSTALLISATIONS 
Some of the most remarkable varieties of forms hitherto 
observed in copper-pyrites are the following : 
1. P. fig. % The pyramid of 109^ 53', 108^ 40', with- 
out any additional face. Commonly the alternating 
faces of this form are larger than the rest, a peculiari- 
ty of certain series of crystallisation, which, for the 
present system, has been called Hemipyramidal in 
Mr MoHs' characteristic. The form thus produced 
is that of fig. 1. ; and it even sometimes happens, that 
the smaller faces disappear entirely, so as to give 
something like a tetrahedron, which, however, in 
reality is only half of an isosceles four-sided pyramid. 
Forms of this kind are very frequent in copper- 
pyrites, though in some cases they appear more strik- 
ing than in others. 
2. P. P-i-1. fig. 7. Sometimes the faces of the latter of 
these pyramids are much more extended than those 
of P. Very distinct specimens of this variety have 
been found in the mine Alte Elisabeth, near Frei- 
berg, in Saxony. 
3. P-— 8. P. fig. 8. The same variety to which Henc- 
kel''s drawings of " Pyrites decaedros"''' refer. 
4 p— L P. p+i» fig. a 
5. P— P-f-L gJ^P-fl. fig. 10. The first of these py. 
ramids is in the same ratio to P— *1, in which P— 1 
is to P. Its axis will therefore be 
terminal edge — 132<> 19'; 
lateral edge = 69® 44'. 
