A Precious Stone is a piece of mineral crystal which is cut and in a polished form. It is used to make jewelry or other adornments. Precious stones can be classified into precious stone and semi-precious stone. However, certain rocks such as lapis lazuli and opal and occasionally organic materials that are not minerals, such as amber, jet, and pearl are also used for jewelry and are therefore often considered to be Precious stones as well. Most Precious stones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. And rarity is another characteristic that lends value to a Precious stones.