 Graphitic varieties are also occasionally found that are very rich in this constituent. In a few places these varieties have been mined as a source of plumbago. The question as to the origin of the magnetite and graphite has not yet been completely solved....  Final Report - Seite 125von New Jersey Geological Survey, New Jersey. State Geologist - 1910Vollansicht - Über dieses Buch
 | University of Illinois (Urbana-Champaign campus) - 1908 - 658 Seiten
...magnetite and graphite has not yet been solved. In some specimens these minerals are completely imbedded in feldspar and hornblende and thus appear to be original....introduced subsequently to the solidification of the rock. ORIGIN OF THE GNEISSES AND THEIR STRUCTURE. Because of their similarity in composition to the acid... | |
 | New Jersey Geological Survey, Geological Survey of New Jersey - 1910 - 568 Seiten
...fragmental quartz grains can be discovered in the rock it is, nevertheless, thought that it was onginafly a sandstone, which has been recrystallized through...the origin of the magnetic ores. (See pages 147 et scq.) ORIGIN OF THE GN'EISSIC COMPLEX. Because of their similarity in composition to the acid gneisses... | |
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