Specific Gravity Test for Gold Specimens and Nuggets
How to calculate the amount of gold in a piece of quartz by formula
G (gold) = (d x N x (1 - q/n)) / (d - q)
G = Weight of gold (grams)
d = Density of gold (approx. 19 gm/cubic cm)
N = Weight of nugget in air (grams)
q = Density of quartz (approx. 2.6 gm/cubic cm)
n = Density of nugget ( gm/cubic cm)
Density = (weight of nugget in air) / (weight in air) - (weight in water)
First determine:
- Weight in air
- Weight in water
In nature gold is never pure and quartz can have all sorts of other impurities included so the results are never exact. Over many years of tests, personal observations have shown that the actual gold content is generally a little more.
You will only know for sure after breaking up the specimen and dollying it up and panning it off.
You would not do this to a beautiful one of a kind specimen but to get an approximate idea on the gold value alone, this formula comes pretty close. You must consider the rock as the contrasting frame presenting the gold in its best original geological setting.
To save you time and possibly making an calculating error, enter your data in this calculator for an answer.
How to obtain the weight in water
You need:
- Electronic Scales
- Stick and narrow board
- String
- Container of water
- Specimen
The set up:
- Place Scale on a narrow board over a table edge, secure firmly.
- Have the scale protruding over the table edge
- Weigh your specimen first and note it down, (dry weight).
- Tie a string to a stick on either end (to tie the specimen to).
- Place stick centrally on the scale with the string loop hanging down.
- Zero out the scale with the stick arrangement on the scale.
- Tie specimen to string loop.
- Hang specimen in water container so that it is totally submerged.
- Weigh your specimen and note it down, (wet weight)
Practice example:
Specimen dry weight : 35.8 grams
Specimen wet weight : 27.9 grams
Result: estimate gold content 17.68 grams of gold
Many thanks to David de Havelland, formula used is from "Gold & Ghosts" Vol.1 pg 9
Another common alternative formula is: