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Use Specific Gravity Test before Hydrofloric Acid...
January 15, 1999 at 20:49:47
If you find a nice gold specimen, like a chunk of quartz laced with gold, it would be unwise to crush it up as collectors will pay much more than its gold content, especially for pieces that show some type of crystallization. You should never guess at the gold content as you could be off quite a bit. Using a specific gravity test is the only way to determine the correct gold content. This procedure is not very difficult. You will need a gold scale with gram weights, a lenght of light thread and a beaker filled with water. First weigh the specimen in air. Next, suspend the specimen in water using light thread and weigh again. Make sure that there are no air bubbles sticking to the specimen as this will give you an incorrect figure. Assuming a purity of 850 fine for the gold, which is about average, and the matrix quartz, a simple calculation can be made. Multiply air weight of specimen by 3.1, then subtract air weight from water weight and the result will be the gold content of the specimen. This figure may be off somewhat if the purity of the gold is significantly higher or lower, if there are voids in the specimen that could trap air or if there are inclusions in the specimens other than quartz like hematite or magnetite. But even if some of these conditions are present, the result will be close enough. This will give you a good idea about how much gold content is in the specimen. You don't want to use acid on a specimen that weighs 5lbs and has only a couple of grains of gold inclosed. Once you have found out how much gold content is locked up in the specimen, then you may want to use Hydrofloric Acid to remove the quartz. Hope this may help.
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