Embedded Files
Classification
Crystal System: Hexagonal
Class: Silicate
Sub Class: Tectosilicate (framework-silicate)
Group: Quartz
Structure and Composition
Composition: SiO2
Structure: The structure of quartz (below) can be represented by connected helical chains of silicate tetrahedrons, a silicon atom surrounded by three oxygen atoms.
Identification In Hand Sample
*The underlined portions are the characteristics I consider most diagnostic to identification
Color: Colorless, purple, rose, red, black, yellow, brown, green, blue, orange, etc.
Luster: Vitreous
Hardness: 7
Streak: White
Specific gravity: 2.65 - 2.66
Common Habit: Hexagonal prismatic crystals
Cleavage: Poor/indistinct
Fracture: Conchoidal
Identification In Thin Section
PPL Properties
Relief: Low positive
Habit/Form: Typically, anhedral, highly irregular in igneous and metamorphic rocks
Color: Colorless, clear (with no alterations), often contains inclusions
XPL Properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I white (color bar below)
Extinction angle: Undulatory
Twins: Absent
Uniaxial/Biaxial: Uniaxial (+)
Quarts (Qtz) under PPL demonstrating low relief
Undulatory Extinction of Quartz under XPL https://commons.wikimedia.org/wiki/File:Quartz-zhaseni.gif
Geologic Occurrence
Quarts can be found in igneous, metamorphic and sedimentary rocks. The largest source of quartz is found in felsic igneous rocks, namely granite-like plutonic rocks. Quartz is also a major constituent of sedimentary rocks like slates and sandstones. Quartz can then be found in metamorphic rocks deriving from either kind of the aforementioned rocks.
Significance
Quartz, being one of the most common minerals on the planet, has been known to humanity in some form for thousands of years. The name κρύσταλλος or kristallos is the oldest known name for what we know as quartz and dates back to 300-325 BCE recorded by Theophrastus. Quartz also has several uses. In its microcrystalline form, flint, quartz was an important material for tool making for our oldest ancestors. The conchoidal fracture of this quartz allowed the flint to be broken into sharp points for arrows, spears, axes, etc. Other forms of quartz, particularly colored forms like amethyst, is used as decoration and jewelry even today!
Page updated
Google Sites
Report abuse