A crystal that is precious usually due to a combination of its colour, transparency, lustre, hardness and rarity Gems are usually cut in such a way as to maximise the reflection of light within them, and so make them 'sparkle'
attractive minerals used as jewellery A diamond free of flaws, as far as can be determined by a trained observer with the aid of a 10-power magnifying glass, and having a colour and other characteristics that do not deleteriously affect its value for use as a faceted ornamental diamond
art highly prized for its beauty or perfection a crystalline rock that can be cut and polished for jewelry; "he had the gem set in a ring for his wife"; "she had jewels made of all the rarest stones
If you describe something or someone as a gem, you mean that they are especially pleasing, good, or helpful. a gem of a hotel, Castel Clara Miss Famous, as she was called, was a gem. ground-effect machine