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Group A. Isolates gems with a specific gravity of 4.7963 and over 4.70; in this group is placed zircon, with a specific gravity of from 4.70 to 4.88. Group B. Stones whose specific gravity lies between 3.70 and under 4.7963. Garnets, many varieties. Almandine 4.11 and occasionally to 4.25 Ruby 4.073 ” 4.080 Sapphire 4.049 [...] The fixing of the specific gravity of a stone also determines its group position with regard to weight; its colour and other characteristics defining the actual stone. This is a safe and very common method of proving a stone, since its specific gravity does not vary more than a point or so in different [...] |
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