A simple test for gold

Hydrochloric acid is sometimes called muriatic acid when it is in dilute form.  The dilute acid can be used as a simple test for gold.

Sometimes it is a case of not being able to see the forest for the trees, and sometimes I am guilty of this fault among the many others I have. Gold is not called the noble metal because it is used to make crowns, but because there are very few things that can cause it to dissolve. Aqua regia, a mixture of one part of nitric acid and three parts of hydrochloric acid is one of them. It can also be dissolved in a solution sodium cyanide, and a few other compounds.

There are very few minerals that resemble gold alone and a few sulfides that are commonly called fools gold. Some weathered mica can also resemble gold if these substances are treated with acid they will dissolve and emit an odor like rotten eggs. You can use ordinary vinegar to make this test if you want, but muriatic acid works even better. You can buy this acid at a local mason supply store or some times at your local hardware store. Another source of acid can be found in your local auto parts store under the name “battery acid.” Battery acid is a dilute form of sulfuric acid, but any of them will work for this test.

If the material forms than crystals, and it is the color of gold is most probably fools gold. When acid is supplied to this material it will make a gas called hydrogen sulfide is smells just like rotten eggs, you can't miss it. Gold is not affected by any of these acids, nor does it create a smell. This is not to be considered a definitive test for gold, but it sure eliminates in a real hurry many things that do look like gold.

Weathered mica is one of the few things that may not eliminate, but the reaction when acid may bleach the iron staining that makes it look like gold. In any event weathered mica is about nine times lighter than real gold. The only other metals that are not affected by acid are the platinum group metals because they are also considered to be noble metals.

Gold and platinum are often found together so much so that the early Spanish Conquistadors in Peru used platinum as an alloy in their coinage because they had no value for platinum. During the 20th century many of the Spanish coins were dissolve so their platinum content could be recovered.

This test can be used on both gold that is visible to the naked eye, and gold that is only visible under a microscope. It is best to draw a circle around microscopic specimens with a pencil so you can find them again. The graphite in a pencil is not affected by any acid, but don't use a ballpoint pen because the eight may be affected by the acid.

Something else that can be added to your prospecting equipment is a dropper bottle for holding the acid allowing you to dispense it one drop at a time. For many tests all you do this a single drop of acid. This test is also useful for finding out if a stone as limestone or not. In the presence of calcium carbonate it fizzes.  It doesn't affect Quartz, but gold is often found in either mineral. Occasionally it is also found in Jade as flecks of gold.