Diamonds
Diamonds are definitely the No. 1 gem in the world. Diamonds are created at the core of volcanoes during intense eruptions. The intense heat is responsible for the beautiful crystalline form of this carbon mineral. Over long periods of time, diamonds slowly change to graphite, another carbon-based crystalline form that is very different in appearance from a diamond.
Rubies, Sapphires and Emeralds
These three crystalline gemstones certainly belong on the list of popular and valued rock crystals. As gemstones, they are always ranked in the top 10, often in the top five. Their name recognition and popularity are excellent. Each of these minerals forms beautiful colorful crystals that at times can exceed the price of diamonds. Rubies are known for their red color, emeralds as being green and sapphires as blue. Yet colors of these stones can vary, especially with the sapphires.
Rock Gems
So far, only gems containing one outstanding mineral crystal have been mentioned. Nonetheless, a rock is sometimes defined as a substance containing more one than one mineral. This would include rock gems, precious gems that are also rocks, which contain at least two minerals. Lapis lazuli is a classic example of a rock gem, for it contains several minerals, including pyrite (fool's gold) and lazurite, a copper mineral, which gives the stone its spectacular blue color.
Four More Crystalline Gems
So far, the list of popular rock crystals has been mostly drawn from birthstones. Not all birthstones are crystals; for example, opal, which has an amorphous shape. However, crystal birthstones such as garnet, amethyst, topaz and aquamarine are all very popular and could easily be included in the top 10.
Last and Least
Last and perhaps least is a form of crystal that actually goes by the name of rock crystal. In reality, rock crystal can be used to classify a form of colorless quartz. Nonetheless, rock crystal is inexpensive, attractive and popular. The common variety is sometimes used as a fake diamond, while rare complex crystals of this variety of quartz can outprice some diamonds.