Gemstones -

While the 4 Cs are famously used for diamonds, they apply differently to colored stones where is the most critical factor.

Gemstone Buying Guide - The National Association of Jewellers GEMSTONES

: A broad category for all other stones, including Amethyst , Topaz , and Opal . Organic Gems : Non-minerals like Amber , Pearl , and Jet . The "4 Cs" of Gemstone Value While the 4 Cs are famously used for