Gold and silver coins have an intrinsic value of the precious metals they contain. This is regardless of condition -even if they are too poor to be a collecter's coin.
Gold and silver prices are usually quoted in troy ounces, which is different to the avoirdupois (common) ounce. A troy ounce is 31.10 grams and an avoirdupois ounce is 28.35 grams. Just to make it more confusing a troy pound is 12 ounces and is less mass than a common pound of 16 ounces.
Anyway, to make it simple, you need two pieces of information;
•current gold or silver price -usually quoted in US dollars per troy ounce. This can be found at www.kitco.com/.
•current value of Australian dollar, relative to US dollar. This can be found at www.rba.gov.au/statistics/exchange_rates.html.
Then, divide the metal price by the exchange rate and divide again by 31.10. You then have the value of the metal in Australian dollars per gram. Why grams? Because that is the most common unit for specifying mass of coins.
For example, on 6 February, 2009 silver price was quoted at US$13.11/ounce and exchange rate 0.6521 AU$ per US$. Apply the simple formula and you get silver valued at 64.6¢ per gram. A 1966 50¢ piece is 13.28 grams, 80% silver; so it contains 10.624 grams of silver. Multiply that by the value you just calculated and you get a silver value of $6.87 for a 1966 'round'.
Now, to make life easier for you, here are precious metal contents of some better known Australian bullion coins;
•Half sovereign contains 3.661 grams of gold
•Sovereign contains 7.322 grams of gold
•$200 gold coins (1980 to 1994) contain 9.167 grams of gold
•Threepenny bits, 1.304 grams of silver up to 1944 and 0.705 grams from 1946. Australian silver coins were changed from sterling silver (92.5%) to 50% silver in 1946.
•Sixpences -2.618g & 1.415g
•Shillings -5.226g & 2.825g
•Florins -10.462g & 5.655g
•1937, 1938 Crowns have 26.150 grams of silver
•and you have already seen, in the example above, 1966 50¢ contains 10.625 grams of silver.
Knowing this you can calculate the bullion value of any coin. Also applies to coins from other countries, other currencies and other metals (for example, some special issue Australian coins were platinum). You only need to know metal price, coin weight & metal percentage (if you don't have a coin catalogue, try Google) and the current exchange rate for your chosen currency.
Also, the same principles apply to jewellery. If your gold chain is 22 carat (91.67% pure gold -incidently ebay's own guide doesn't mention the gold percentage of a very common fine gold alloy) then you can easily obtain a value for the gold once you have weighed it. Of course, the age, design, craftsmanship and condition will all influence total value but, it can never be less than the precious metal value.
I hope this helps someone