a brilliant adamant

This faceted gemstone seems to capture the faintest glimmers of light, and to transform them into marvellous rainbows. Truly this must be the legendary adamant, harder and brighter than diamond; a jewel not made by the forces of nature, but crafted by one of the great Noldorin smiths - Celebrimbor, or perhaps Feanor himself.

It is a brilliant adamant.
It weighs a few ounces.

You identify a brilliant adamant.
It weighs four ounces, and it is worth about fifty lauren.
Its keywords are adamant, gemstone, jewel, and gem.