At Butte for instance, secondary chalcocite is clearly to be recognized.
"The Economic Aspect of Geology"
C. K. Leith
No traces of other primary minerals are present and the chalcocite here is regarded as probably primary.
"The Economic Aspect of Geology"
C. K. Leith
The primary copper mineral in the limestone is chalcocite, in exceptionally rich and solid masses, showing no evidence of having replaced earlier sulphides.
"The Economic Aspect of Geology"
C. K. Leith