How to test specific gravity, and why it actually matters

Specific gravity (SG) compares how dense a material is relative to water, and it is one of the most reliable field tests you can do because two minerals that look almost identical can have very different densities. The basic method: weigh the dry specimen in air, then weigh it again while it is fully submerged in water (suspended by a thread so it is not touching the container), then calculate SG as weight in air divided by (weight in air minus weight in water). A kitchen or jeweler's scale accurate to a tenth of a gram is precise enough for most hobby purposes. Some reference points worth memorizing: quartz sits around 2.65, most common rock forming minerals cluster in the 2.5 to 3.5 range, hematite is around 5.3, pyrite is around 5.0, and native gold is around 19.3, dramatically higher than almost anything else you will find in a stream. This is exactly why SG is the most reliable way to separate gold from pyrite or mica when color alone is not convincing.