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Publication — identifier 0034 [Johnson, M. L., McClure, S. F., DeGhionno, D. G. 1996]
Johnson, M. L., McClure, S. F., DeGhionno, D. G.
Some Gemological Challenges in Identifying Black Opaque Gem Materials
Gems & Gemology 32 (4): 252—261
Among the most difficult gems to identify are those that are black and opaque. To identify a black opaque material, every possible mineral, and many rocks and manufactured substances, must be considered.