Pratt, W. P. (1995). The Midcontinent strategic and critical minerals project. US Geological Survey circular 1124.
Παραπομπή Chicago StylePratt, Walden P. "The Midcontinent Strategic and Critical Minerals Project." US Geological Survey Circular 1124 1995.
Παραπομπή MLAPratt, Walden P. "The Midcontinent Strategic and Critical Minerals Project." US Geological Survey Circular 1124 1995.
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