Bulletin . .05 23a_ (B) Photomiciograph of a portion of the same section shown in (A), but veryhighly magnified in order to show the intricacy of tlae reticulated gray = chalcocite. Dark gray = bornite. VIUGINIA GEOLOGICAL SLUVKV, PLATE .) (Aj Photomicrojirapli of u polished sfetion of ore inmi ( onilicld Irospect No. reticulated interjiiowtli of bornite and t-lialcocite. By etching thesection it shows ch-aily tiiat the minerals are intergrown along crystallo-graphic directions. 8ucli occurrences as this add to the difhculty of account-ing for the formation of th
Bulletin . .05 23a_ (B) Photomiciograph of a portion of the same section shown in (A), but veryhighly magnified in order to show the intricacy of tlae reticulated gray = chalcocite. Dark gray = bornite. VIUGINIA GEOLOGICAL SLUVKV, PLATE .) (Aj Photomicrojirapli of u polished sfetion of ore inmi ( onilicld Irospect No. reticulated interjiiowtli of bornite and t-lialcocite. By etching thesection it shows ch-aily tiiat the minerals are intergrown along crystallo-graphic directions. 8ucli occurrences as this add to the difhculty of account-ing for the formation of the graphic intergrowths as characteristic of theVirgilina ores. In the present instance there are reasons for believing themto have resulted from su])ergene agencies, but there is no proof that they arenot of hypogene origin and that tlie two mincials were ilcposited contem-poraneously. Light gray ^= chaicocite. Dark gia\ = boitiite. DETAILED DESCEIPTION OF THE VEINS AND ORES. 93 A second theory is, that the bornite in the intergrowths is a primarymineral and of hypogene origin, and that the chalcocite represents asecondary alteration of the bornite but that it is of hypogene origin. Thatis, the adherents of this theory believe that the chalcocite is a
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