Amethyst has historically been the most prized gemstone in the quartz family. It is treasured for its purple hue, which can range in tone from light to dark. Emerald: Emeralds are one of the three main precious gemstones (along with rubies and sapphires) and are known for their fine green to bluish green color. They have been treasured throughout history, and some historians report that the Egyptians mined emerald as early as 3500 BC.