OF COPPER-pyHITES. 
5 
regular octahedron, or, more properly, from the tetrahedron. 
The latter even alleges cleavage to take place parallel to the 
faces of the tetrahedron, and gives the Caractere geome- 
trique of Cuivre pyriteuoc thus : 
" Forme primitive. Le tetraedre regulier, (fig. 78. pi. Ixx.) 
Quelques cristaux offrent des indices de lames paralleles 
aux faces de ce solide." — Traite, t. iii. p. 530. 
The forms he describes as modifications of the regular 
tetrahedron, and others in connection with it, moreover 
under the denomination of Cuivre pyrlteux trcmspose^ the 
twin-crystal mentioned above, which he compares with those 
of spinel. 
Rome' de l'Isle, in order to give a distinctive character 
between the hexahedral iron and the pyramidal copper- 
pyrites, states the crystals of the latter always to possess the 
form of tetrahedrons, more or less modified. Crystallo- 
grapJiie^ t. iii. p. 310. 
But, says Hauy, sometimes copper-pyrites is observed 
in the form of the octahedron, perfectly regular ; and since 
this form is equally found in iron-pyrites, the line of de- 
marcation disappears. Traite, t. iii. p. 534. 
The mineralogical works, according to the Wernerian 
method, infer uniformly copper-pyrites to have tessuiar 
forms, describing them as tetrahedrons, octahedrons, &c. 
From a comparison of all the preceding, and of many 
other mineralogical books, it appears that none but Henc- 
kel's could excite even a suspicion that the form of the 
present species is pyramidal; and thus our endeavours to- 
wards the advancement of truth, in this particular, as well 
as in Natural History in general, will be the less subject to 
errors, the more strictly we follow the advice of that intel- 
ligent natural philosopher, in deriving our knowledge of the 
natural productions from the observations of those objectfe 
themselves. 
