Description: One of the most common minerals found in the Earth's crust. If pure, quartz forms colorless, transparent and very hard crystals with a glass-like luster. A significant component of many igneous, metamorphic and sedimentary rocks, this natural form of silicon dioxide is found in an impressive range of varieties and colours, including jasper, flint, tiger’s eye, citrine, chalcedony, onyx, opal and agate.
Chemical Formula: SiO2
Crystal Form: 7 basic crystallographic forms, the hexagonal prism and trigonal rhombohedra are very common
Crystal System: Trigonal
Color: Varieties are colorless, purple, rose, red, black, yellow, brown, green, blue, orange, etc.
Streak: Colorless (harder than the streak plate)
Luster: Vitreous (glass-like) in crystals, massive forms are dull or waxy
Fracture: Conchoidal
Cleavage: None - typically breaks with a conchoidal fracture.
Hardness: 7 on Moh’s scale.
Density/Specific Gravity: 2.6 - 2.7 g/cm3
Magnetism: N/A
Taste: N/A
Hydrochloric acid: N/A
Radioactivity: N/A
Fluorescence: N/A
Distinguishing Physical Properties:
Hardness: (easily scratches glass, also harder than steel)
Luster: glass-like
Fracture: conchoidal fracture in crystals, in massive specimens the fracture often looks irregular to the naked eye, but still conchoidal at high magnification.
Cleavage: poor to indistinct cleavage
Photograph Attribution: Quartz specimen photograph by Sean C. Murphy, 2020.