Rock Crystal

Rock crystal is the official name given to what most people call quartz (”Quartz” covers a large umbrella of different minerals. Varieties of quartz are distinguished only by differences in the individual crystals on a molecular level). It is the most common mineral on the planet, since most sand and other rocks are made of rock crystal.

One interesting thing about rock crystal is that it is piezoelectric. This feature gave rock crystal’s first commercial success as phonograph needles. It is most commonly used today in watches, internal clocks for computers and as frequency stabilizers for radio transmitters.

Color: Colorless

Color of streak: White

Moh’s hardness: 7

Density: 2.65 grams/cubic centimeter

Cleavage: None

Fracture: Conchoidal, very brittle

Crystal system: Hexagonal prisms

Chemical composition: SiO2, silicon dioxide

Transparency: Transparent

Refractive index: 1.544-1.553

Double refraction: +0.009

Dispersion: 0.013 (0.008)

Pleochroism: Absent

Absorption spectrum: None

Fluorescence: None

Rock crystal can be synthetic.