Wallis, K. (2006). Gemstones: Understanding, identifying, buying. Antique Collectors' Club.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रWallis, Keith. Gemstones: Understanding, Identifying, Buying. Woodbridge: Antique Collectors' Club, 2006.
एमएलए (9वां संस्करण) प्रशस्ति पत्रWallis, Keith. Gemstones: Understanding, Identifying, Buying. Antique Collectors' Club, 2006.
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