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Gold / Quartz Specific Gravity... Question

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The formula I`ve used is wet weight which is for water X SG of quartz which is 2.6 (water SG is 1, wet weight is weight of water displaced) take that away from the dry weight and it "should" give you the weight of what has a SG above quartz. If speci is only quartz and gold then that is the weight of the gold. For this one that would be  

70 x 2.6 = 182      242-182=60 thus 60 grams of gold if speci is only gold and quartz. Quartzs SG is apparently a whisker under 2.65 but as we can really only guesstimate this 2.6`ll do.

But having said that I`ve yet to find it is only a guestimate but usually pretty close, the dolly pot gives the accurate answer. 

Edited by Norvic
add4ed clarification
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I got 62.39 using this formula:

(SG -2.65) x 19.3 / (19.3-2.65) x SG

          That result is 14.629/56.743, which gives .2578, or 25.78% gold, which equals 62.39 grams

SG of the specimen is 3.408

Jim

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9 hours ago, Norvic said:

The formula I`ve used is wet weight which is for water X SG of quartz which is 2.6 (water SG is 1, wet weight is weight of water displaced) take that away from the dry weight and it "should" give you the weight of what has a SG above quartz. If speci is only quartz and gold then that is the weight of the gold. For this one that would be  

70 x 2.6 = 182      242-182=60 thus 60 grams of gold if speci is only gold and quartz. Quartzs SG is apparently a whisker under 2.65 but as we can really only guesstimate this 2.6`ll do.

But having said that I`ve yet to find it is only a guestimate but usually pretty close, the dolly pot gives the accurate answer. 

You lads over there would have the advantage on us as to nuggets found with a detector and specific gravity calculations I suspect.  Your dolly results are the proof that we sometimes never see.  Hard rock gold is often times not tested before crushing and that is not found with a detector.

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Such determinations are subject to two things:  assumptions and measurement uncertainty.  Here both are present, although the assumptions likely outweigh the measurment uncertainties in this case.

The density of naturally occuring gold is not fixed, because it's not pure gold (what most assume) but rather an alloy of gold and other metals.  Those other metals are typically copper and silver, but there are several other metalic elements which will alloy with gold (which in most cases reduces the density of the alloy to a value below that of pure gold).  So in reality you have many metals in the metallic part of the 'nugget'.  Bottom line is that assuming the gold part has a density of 19.3 g/cc (or equivalently a specific gravity of 19.3) is erroneous.  Further, the density of quartz varies, not pure silicon dioxide crystal, but when you include impurities and voids, there is no magic number.

Measurement uncertainties can take multiple forms as well, but the most likely two culprits are precision and accuracy.  Accuracy is related to how 'off' a measurement is compared to a standard source.  If your scale reads 151 g for a sample and 149 g for a standard (known, calibrated) weight of 150 g then you have to correct the 151 g.  Most people don't bother buying standards to calibrate their scales, they just assume the scale is reading accurately.

The second part -- precision -- results from the least significant amount of readout the scale provides.  Suppose you have a scale which only reads out in single grams (without any decimal places) and you measure 7 grams.  Suppose you also have 7.00 grams of standard and confirm that those standards also give a reading of 7 grams.  You've done the calibration (that's good) but consider that if you put a 6.51 g specimen or a 7.49 g specimen on the scale, each would also read 7 g.

Finally, how sure are you that the specimen contains quartz as opposed to some other mineral such as calcite?  And could it possibly have more than one mineral present?  All of these issues together must be kept in mind when reaching a conclusion of the amount of gold present.

 

 

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everything you say GB_Amateur is correct, and any SG on a "Gold in Quartz" specie is at best an indication that you can expect to get some gold from the specie when it's processed.  From my experience sometimes the calculations are close to the mark and other times not so, and as always the dolly pot tells the truth. 😁

cheers dave

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GB you`ve nailed it, never has the sale results from the mint come back without there being an allowance for silver value that is from a pre-smelted ingot, never has the weight of the gold plus the silver added been equal to that ingots weight sent. Copper usually making up most of that weight. Then when the crushed specimens left-overs are examined there is many other minerals, in my area always some ironstone and also likely some antimony with other unidentified minerals also present. I have never seen just quartz and suspect that would not be possible.

That is why being precise with your measurements will achieve little, we as hobbists can only guestimate. Whoops Davsgolds replied but I`ll leave my post as is.

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Thanks GB_Amateur

I have a specimen that is considered to have 8ozt of gold.  When you shoot it with an RF gun the gold is somewhat less than pure.  I've seen ranges from 85 to 95% so just as there is no pure quartz there is no pure gold in the field.

Field testing and sampling requires an assay and then you find out what was in a rock/specimen after the fact.  Then you could say you wish you had kept it in the original form.

The large nuggets/specimens just found in Australia will have many ounces of 'impurities' in them that could affect their value but probably not much because they are unique and collector's items now.

Mitchel

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If you have a (professional) use hydrofloric acid. You will know how much gold you have and preserve the specimen somewhat.

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14 hours ago, Walker said:

If you have a (professional) use hydrofloric acid. You will know how much gold you have and preserve the specimen somewhat.

I think you are right, looking for someone now...I really want to see what's inside.

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Tis a bit of a bummer leaving as is and not knowing how much golds in specis, but as Walker says you can preserve it somewhat with hydrofluoric, there is some cleaners available in hardware stores that have diluted hydrofluoric acid in them. Depending on the specimen how long the diluted acid takes sometimes months. I remember this procedure has a thread on it somewhere in this forum, a search should locate it.

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