Here are some plans I drew to make a simple scale to measure the specific gravity of an item. Specific gravity can help in the identification of rocks, and can even be used to measure the purity of a gold or silver object, as well as in the authentication of coins, especially gold and silver coins.
Specific gravity is the difference in mass between water and any other object.
Gold for instance is about 19.3 times heavier than an equal volume of water, and it doesn't matter if you are dealing in pennyweight, grams, pounds or tons, it is always the same formula. Check it out if interested, and drop me a note if you have any problems figuring it all out.