Quartz and rock crystal are both abundant minerals found throughout the world in the Earth's crust. According to Mindat.org, "Quartz is the most common mineral found on the Earth's surface." Quartz and rock crystal are composed of silicon dioxide and are found as components within many different types of rocks.
There are dozens of different types of quartz. Mineral Data Publishing states that quartz is predominantly silicon dioxide with traces of other elements. The different types of elements present in the quartz will determine its characteristics and classification. For example, if a quartz sample contains high amounts of dumortierite, a type of mineral, it will take on a red and pink hue and be classified as rose quartz.
Mindat.org states that rock crystal is a "transparent, colorless variety of quartz." It is also known as Alaska diamond or mountain crystal. Rock crystal does not contain enough trace minerals to affect its coloration, so it appears clear.
When molten rock, or magma, begins to cool beneath the Earth's surface the various minerals found within the magma begin to crystallize. If silicon dioxide cools to a temperature below 573 degrees Celsius it will begin to crystallize into quartz or rock crystal. Depending on the concentration of other minerals within the silicon dioxide, different types of quartz will form.
Quartz and rock crystal are used in several industrial capacities. They are used as a component for optical instruments and for making glass. The silica within these crystals are also used in concrete setting. According to Geology.com, since quartz has electrical properties and resistance to heat, it is often used in electrical products such as cell phones and navigation devices.
Quartz has been used throughout ancient history in art and sculpture. Some of these pieces are still bought and sold today. The Association for Archaeology and Anthropology are selling a 5,000-year-old quartz earring from ancient Samaria. The author Lois Fruen states that quartz sand crystals were used by the Egyptians to develop glass making in 1500 BC. Ancient artists considered glass a semi-precious material since it was rare and difficult to make.