You can find quartz nearly anywhere you look. Quartz is made of silicon and oxygen, which are among the planet's most abundant elements. It is formed from the magma that creates igneous rocks and appears in a variety of colors, including blue-white, yellow, green, red and milky white. Some quartz is even transparent. Some forms of quartz, such as amethyst, jasper and citrine, are often seen in jewelry as semi-precious gemstones. When clear quartz crystal is allowed to form unobstructed it assumes a hexagonal symmetry and can grow to large size.
All quartz and all glass are silicon dioxide. This hard substance has one silicon atom and two oxygen atoms forming its molecular structure.
Quartz comes in two basic forms, according to Dr. Renn Tumlison of the biology department at Henderson State University in Arkadelphia, Arkansas. Micro-crystalline quartz has a crystalline structure that is too small to see with the naked eye. Macro-crystalline quartz is formed with a structure of large crystals. Both forms of quartz flake or fracture in a conchoidal or ring-like pattern. This is a characteristic of quartz that humans have learned to exploit.
Micro-crystalline forms of quartz include agate, chert and chalcedony. Micro-crystalline quartz is formed of volcanic silica. Agate is used as a semi-precious stone for making jewelry. It forms when volcanic silica, ash, water, iron and other minerals combine under pressure deep in the earth. The iron content gives agate its golden brown hues.
Chalcedony is a type of chert quartz also used as a gem. It is seen in red, blue, green and rusty orange colors and has a waxy luster. Chalcedony also has a waxy luster and is commonly seen in blue-white, buff and tan. This type of silicate material is also found in petrified wood. Rainfall washes dissolved minerals into the pores of a tree and the minerals dry out and replace the wood.
Chert in its various forms is useful to humans in the manufacture of tools and weapons. Native Americans used chalcedony to form spear points and tools ten thousand years ago, according to Minnesota State University.
Macro-crystalline quartz is often used in jewelry making. This form of quartz has large crystals easily visible to the human eye. Amethyst, citrine, rosy quartz and clear rock crystal are all macro-crystalline quartz.
Citrine quartz has high luster, an attractive green color and is often used as a gemstone. Amethyst also is gem quality quartz and can come in a pale lavender color. When cut into faceted gems, citrine quartz stones are often made into expensive jewelry.
Some quartz stones can become very large. Rosy quartz has a pale reddish-pink color and is often found in massive formations. Rock crystal quartz is used in the making of quartz watches. The tiny quartz tuning fork inside a watch vibrates thousands of times per second in response to an electrical current.