Leonard James Spencer

“ Analyses usually, however, show the presence of more iron, owing to the intimate admixture of iron-pyrites. Traces of gold, silver, selenium or thallium are sometimes present, and the mineral is sometimes worked as an ore of gold or silver. ”

“ Twinning according to the second law can only be explained by reflection across the plane (101) , not by rotation about an axis; chalcopyrite affords an excellent example of this comparatively rare type of symmetric twinning. Interpenetration twins (fig. 2) with (110) as twin-plane are of very rare occurrence. ”

“ Crystals are usually tetrahedral in aspect, owing to the large development of the sphenoid P {111}. The faces of this form are dull and striated, whilst the smaller faces of the complementary sphenoid P′ {111} (fig. 1) {{img float |align=left |width=252px |file=EB1911 Copper Pyrites.jpg |cap= Fig. 1.⁠Fig. 2. are bright and smooth. ”