Gold Specimen Calculations

Calculating Weight of gold in a Specimen! The Specific Gravity Test (used to calculate the gold content of gold nuggets that contain a mixture of gold and other materials) In this example of the specific gravity test, we use gold mixed with quartz. Simply put, the formula is 3.1 x the weight in water, minus 1.9 x the weight in air:

Wet nugget weighs 74.5 grams x 3.1 = 230.95
Dry nugget weighs 96 grams x 1.9 = 182.4

230.95 - 182.4 = 48.55
31.1 = number of grams per ounce
48.55 / 31.1 = 1.56 ounces of gold

Original dry weight = 96 grams / 31.1 = 3.08 ounces.
Subtract the difference between the wet and the dry:
3.08 ounces - 1.56 ounces = 1.52 ounces.
Therefore what is left is 1.52 ounces of quartz.

"Wet" = weight in water - Put container of water (enough water to cover nugget) on scale. Tare (zero) out scale. Hang nugget by string in water. Note weight.

The specific gravity for gold is 19.3.
The specific gravity for quartz is 2.65.
The ratio between gold and quartz is 7.28 X.

What is specific gravity? Specific gravity is simply the weight in grams of one cubic centimeter of a metal. Here are specific gravities and other properties of a few more metals:
 Metal Symbol Specific Gravity Copper Cu 8.96 Gold Au 19.32 Iron Fe 7.87 Lead Pb 11.34 Nickel Ni 8.90 Palladium Pd 12.00 Platinum Pt 21.45 Silver Ag 10.49 Example 2

The measurement we really need to find is volume and this can easily be done if you have a digital scale. Take a glass or cup that is big enough to hold the rock and fill it with water so that the rock will easily be covered with water when placed in the vessel. Tie a thin piece of string around the rock such that it can be suspended in the water in the vessel so that it is not touching the bottom nor sides and is fully submerged. Now place the vessel with water without the suspended rock inside and weigh. Now add the suspended rock and determine the increase in the weight on the scale. This can either be done by zeroing out (tareing) the scale after the first measurement or by subtracting the first weight from the second. This number represents the volume of the rock in cubic centimeters since while the rock is suspended it is displacing an equal volume of water and mimicking its density which is 1 gram per cubic centimeter. Therefore the increase in the weight in grams on the scale equals the volume of the rock in cubic centimeters. when you get this number it is easy to plug into a formula for determining a fairly accurate estimate of the gold content. A piece of quartz of equal size (33.3 cubic centimeters) should way 88.25 grams since quartz has a density of 2.65. The formula for determining gold content in a quartz matrix is: 3.1 x weight of rock in water minus 1.9 x weight of rock in air The peice we use as an example here is 95.1 grams quartz & gold specimen If there are minerals in the rock heavier than quartz like iron oxide then the estimate will run high. From past experience I tend to think this formula runs a bit high anyway and that the first number should be between 3 and 3.05. Using this formula in your instance comes up with: 3.1 x (95.1 - 33.3) - 1.9 x 95.1 = 10.89 grams of gold . 