Where is Quartz in host rock found?
Quartz (SiO2) with associated rock
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Open the appQuartz in host rock occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Quartz in host rock
Worldwide
Quartz is one of the most common minerals on Earth and can be found in virtually every country and geological setting. Notable occurrences of specific varieties or large crystals include Brazil (amethyst, citrine), Arkansas, USA (clear quartz), Switzerland (smoky quartz), and Madagascar (rose quartz). As a constituent of common rocks like granite and sandstone, it is globally distributed.
Igneous Rocks
Common in felsic igneous rocks such as granite, granodiorite, rhyolite, and pegmatite. Look for it as glassy, often anhedral grains among feldspars and micas.
Metamorphic Rocks
Abundant in metamorphic rocks like quartzite (nearly pure quartz), gneiss, schist, and granulite. In these rocks, it often forms recrystallized grains or lenses.
Sedimentary Rocks
The primary component of sandstones and siltstones. Also forms as chert, flint, and jasper, which are microcrystalline varieties found in sedimentary sequences, often associated with marine environments.
Hydrothermal Veins
Commonly found in hydrothermal veins, often associated with metallic ore deposits (e.g., gold, silver, copper). These veins can contain large, well-formed quartz crystals.
Collecting tips
- Hardness Test. Quartz is harder than steel (Mohs 7). If you can scratch glass or steel with the mineral, it's likely quartz or a harder mineral. This helps distinguish it from softer minerals like calcite (Mohs 3).
- Conchoidal Fracture. Look for characteristic conchoidal (shell-like) fractures, especially on broken surfaces. This is a key diagnostic feature as quartz lacks cleavage.
- Luster and Transparency. Observe the vitreous (glassy) luster and, if possible, its transparency. Even in host rock, individual quartz grains often show a glassy sheen.
- Crystal Form (if present). If well-formed crystals are present, look for the characteristic hexagonal prism terminated by rhombohedra. This is more common in vugs or veins within the host rock.
- Absence of Cleavage. Carefully examine broken surfaces for any flat, parallel planes of cleavage. The absence of cleavage is a strong indicator for quartz, differentiating it from feldspars which have two distinct cleavage planes.
- Chemical Inertness. Quartz does not react with dilute hydrochloric acid, unlike calcite or dolomite. This is a useful test to distinguish it from carbonate minerals.
Quick Check
- Color:
- Variable (colorless, white, pink, purple, yellow, brown, black)
- Luster:
- Vitreous to greasy
- Streak:
- White
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