Quartz

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, red or yellow jasper or white-black banded onyx. Quartz often occurs in granite, sandstone and limestone.

Some quartz crystal structures 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: 2.203 g/cm³
• Hardness: 7
• 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