More than 4,000 naturally occurring minerals—inorganic solids that have ... and emeralds continue to qualify as "precious." (At one time, amethyst was also considered a precious gem, but large ...

You can get a good idea of a crystal's structure by looking closely at just a small piece of it, as the repeating units all follow the same ... mineral. Some gemstones are crystals, such as ...

Semi-Precious Gems: Include amethyst, turquoise, garnet, and many other beautiful stones that don’t command the same high prices. While most gems are mineral-based, some, like pearls ...