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Australia | |
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| Steve Sorrell collection |
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Belgium | |
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Egypt | |
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Germany | |
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| Rocks & Min., Jan/Feb. 1980 |
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| Th. Thieme collection |
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India | |
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| Current Science 75 (8): 763 (1998) |
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Japan | |
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| http://cam.arts.usf.edu/McCollumPDF/16.VoltTrig.pdf. |
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Libya | |
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Netherlands | |
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Russia | |
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| http://camb.demonhosting.co.uk/JConfAbs/6/PCM3.pdf. |
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UK | |
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USA | |
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| Jour. Geol., 54, no. 2, 117-122 (1946) |
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| Lunar and Planetary Science XXXIV (2003) |
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| Rocks & Min., Jan/Feb. 1980 |
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| AmMin 10:152-155 |
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| Rocks & Min: Nov, 1945. |
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| California Geology, Nov. 1986. |
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| Am Jour. of Science, 4th ser. vol. 7 no. 43, (July 1899) |
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Western Sahara | |
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| A. M. I. Martins collection |