Precious metal refers to a kind of metal with high economic value and relative scarcity. The main precious metals include gold, silver, platinum and palladium. Generally speaking, precious metals are characterized by relatively small corrosion and good electrical and thermal conductivity, and are widely used in industry and jewelry making.

Heavy precious metals and light precious metals are usually distinguished according to the density of metals:

1. Heavy precious metals: generally refers to precious metals with high density, mainly including platinum and palladium. Platinum and palladium are silvery white metals with high density, so they are classified as heavy precious metals.

2. Light precious metals: generally refers to precious metals with low density, mainly including gold and silver. Gold is the lightest precious metal, and silver is slightly heavier, but it is still lighter than platinum and palladium.

This classification is mainly carried out from the perspective of density, because density is the ratio of mass to volume of substances, and the density of precious metals will have an impact on their appearance and use in many applications, such as jewelry and coinage.

It should be noted that this classification method is mainly used for simple distinction. In fact, the classification of precious metals may also involve many factors such as their chemical properties and uses.