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these are strange phenomena and
 

image

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Plate XIII. A.
Photomicrograph of a polished section of ore from the Seaboard mine. Shows the network of quartz and iron oxide that occasionally occurs in chalcocite veinlets which develop in fractures in bornite. In this structure the chalcocite at the borders of the developing veinlets is fairly pure. The anastomosing network of minute threads of quartz and limonite follow the replacement process very closely and extends its filaments, in many instances almost to the outer edge of the chalcocite.

These are strange phenomena and the writer can not offer an explanation as to their origin and development.

Light gray = chalcocite.
Dark gray = bornite.
Network in light gray = limonite and quartz.

illustrating Francis Baker Laney, The Geology and Ore Deposits of the Virgilina District of Virginia and North Carolina. Bulletin No. XIV, Virginia Geological Survey, 1917.
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13 March 2013
tags: chalcocite; geology, economic; Laney, Francis Baker; phonemena, strange; photo micrographs; rounds