"1915-05-15Z"^^ . "2002-05-17Z"^^ . "John Sinkankas (1915\u20132002) was an honored Navy officer and aviator, noted gemologist, gem carver and gem faceter, author of many books and articles on minerals and gemstones, and a bookseller and bibliographer of rare books."@en . . "John Sinkankas"@en . "Sinkakas, John"@en . . . . "2002Z"^^ . "American gemologist" . "1915Z"^^ .