gem ( jem), n., v., gemmed, gem•ming, adj. n. Jewelrya cut and polished precious stone or pearl fine enough for use in jewelry. something likened to or prized as such a stone because of its beauty or worth:His painting was the gem of the collection.

When someone says “you're a gem” they usually mean that you are special or unique in some way or that you've done something special or unexpected. A “gem” is a gemstone, and each gemstone is both unique and valuable (though some are more valuable than others.)

The phrase "gem of a person" means that the person is a rare and special find. They may be someone who is kind, loving, and generous - or they may be someone with an incredible talent or skill. They are worth treasuring and cherishing, because they are special and unique.

One can do a simple test at home to find out more about the authenticity and value of a mineral. This is because a magnifying glass can be used to check what color the stone is and how sunlight or artificial light passes through it. A gemstone usually has a very intense color and a high refractive index.