Soen, O. I. (1958). The geology, petrology and ore deposits of the Viseu region, northern Portugal .. Drukkerij Holland N. V..
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रSoen, Oen Ing. The Geology, Petrology and Ore Deposits of the Viseu Region, Northern Portugal .. Amsterdam: Drukkerij Holland N. V., 1958.
एमएलए (8वां संस्करण) प्रशस्ति पत्रSoen, Oen Ing. The Geology, Petrology and Ore Deposits of the Viseu Region, Northern Portugal .. Drukkerij Holland N. V., 1958.
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