What Are Precious and Semi Precious Gemstones? When most people think of gemstones, they think of diamonds, rubies, and sapphires. They don't think of phenakite, moldavite, morganite, alexandrite, carnelian, cinnabar, or others. Most people think of precious stones. And semi precious stones like amethyst and citrine come to mind also. So what makes them precious or semi precious? Definition of a Gemstone First, a gemstone or jewel is a mineral that is been cut and polished to sparkle and dazzle. All gemstones are not minerals though. Some are organic like amber and pearl. Today, diamonds, emeralds, rubies, and sapphire are considered precious stones and the rest are semi precious. Why? I have no clue. It's just the way modern society has it and they got their ideas from the Ancient Greeks. Read more here. But gemstones such as Tsavorite, a form of green garnet, can cost more than an emerald. Why? Because some semi precious stones are rare. Gemstone Groups ...