Quartz

Quartz is the second most abundant mineral in the Earth's contnental crust. It is made up of a continuous framework of SiO4 silicon-oxygen tetrahedral, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. The Silicate class is the largest and most interesting class of all the classes. It is devided into groups based on mineral structures: Nesosilicates (single tetrahedrons), Sorosilicates (double tetrahedrons) , Inosilicates (single and double chains), Cyclosilicates (rings), Phyllosilicates (sheets), Tectosilicates (frameworks.) Quartz is a Tectosilicate. Then there are the members of the tectosilicate subclass: The Feldspar Group, The Feldspathoid Group, The Quartz Group, and The Zeolite Group. As you might assume quartz is part of the Quartz Group. All of the minerals in this group are made of SiO2. They do not all share the same properties but are still made of the same thing.

Quartz forms unusual crystals. They form as hexagonal prisms with their base pyramids modified by rhombohedral faces. This makes it Trigonal. The crystals are commonly large, single, and faultless. They are usually prismatic. These crystals may also be in disorganized groups. Crystals frequently twin; a famous twinning habit is the Japanese twin, where two crystals contact at a 90?angle. Quartz crystals can also contain certain "growths". One is a scepter growth, where the top of a crystal bulges out from the rest of the crystal, and another is a phantom growth, where one crystal forms over another, leaving a ghosted form inside.

Besides the industrial uses quartz can be used as jewelry and other gem uses. Crystalline quartz is the most common type of quartz. However, well-developed clear crystals are rare. Clear quartz crystals are called rock crystals. When they are cut as gemstones, they may sparkle as brightly as diamonds.