Quartz is the most abundant mineral on earth (about 12% vol.), made of trigonal-crystallized silica (silicon dioxide, SiO₂), with a hardness of 7 on the Mohs scale. The usually six-sided prisms that end in six-sided pyramids are either colorless rock crystal, or colored gemstones such as violet amethyst, yellow citrine, pink rose quartz, white milk quartz[?], brown or grey smoky quartz[?], leek-green prasiolite[?], grey or white chalcedony, green-grey agate, or red or yellow jasper. Quartz often occurs in granite, sandstone and limestone.

Quartz crystals are piezoelectric and used as oscillators in electronic devices such as quartz clocks and radios.

A non-crystalline glass form of quartz, called fused quartz, can also be produced.

Properties of Clear Fused Quartz

(Based on information in Fused Quartz Catalogue Q-7A, General Electric Company.)

• Density: 2.2 g/cm³
• Hardness: 4.9
• Tensile strength: 48.3 MPa
• Compressive strength[?]: >1.1 GPa
• Bulk modulus[?]: ~37 GPa
• Rigidity modulus[?]: 31 GPa
• Young's modulus: 71.7 GPa
• Poisson's ratio: 0.16
• Coefficient of thermal expansion[?]: 5.5E-7 cm/(cm*K) (average from 20°C to 320°C)
• Thermal conductivity: 1.3 W/(m×K)
• Heat capacity: 45.3 J/mol
• Softening point[?]: ~1665°C
• Annealing point[?]: ~1140°C
• Strain point[?]: 1070°C
• Electrical resistivity: >10¹⁸ Ω×m
• Dielectric constant: 3.75 at 20°C 1 MHz
• Dielectric loss factor[?]: less than 0.0004 at 20°C 1 MHz
• Index of refraction: 1.4585

See also: list of minerals