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chalcocite glances
 

image

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Fig 2.
A bornite crystal from Butte, Montana. This has the crystal form of bornite, but only the exterior is composed entirely of this mineral. The interior is nearly all lattice structure of bornite and chalcocite. x 30 diam.
One of four figures comprising
Plate I.
Photomicrographs of polished sections by reflected light colored to show the actual appearance of the minerals under the microscope.

ex Joseph Murdoch. Microscopical determination of the opaque minerals : an aid to the study of ores (New York, 1916)

Original at Harvard, digitized September 17, 2007. This from the only Plate visible in the scan.

Chalcocite, copper(I) sulfide (Cu2S), is an important copper ore mineral... The term chalcocite comes from the alteration of the obsolete name chalcosine, from the Greek khalkos, meaning copper. It is also known as redruthite, vitreous copper and copper-glance. ¶  ...known to form pseudomorphs — a mineral that has replaced another mineral atom by atom, but [that] leaves the original mineral’s crystal shape intact — of many different minerals...
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10 March 2013
tags: chalcocite; copper-glance; metamorphosis; Murdoch, Joseph; opacity; pseudomorphs