Once you have seen natural gold, it is easy to recognize thereafter. Gold is softer than other rocks. It doesn't rust or oxidize. Normal acids won't dissolve it. All of these things are true, but they don't help the miner or prospector.
Gold is very heavy.
It has a specific gravity of over 19, that is, it is over 19 times heavier than water. Country rock has a specific gravity of 2.5-5, not very heavy at all. The weight of gold is most important in separating it from other materials. When gold is placed in a container with other rocks and minerals, and the container is shaken, the gold tends to go to the bottom, and the lighter rocks tend to come to the top. The speed of this process is greatly increased when water is added to the container.