Where is Quartz varieties and Onyx found?
Quartz (SiO2) varieties and Onyx (SiO2)
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Open the appQuartz varieties and Onyx 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 varieties and Onyx
Brazil
Major source of Amethyst (especially Rio Grande do Sul) and Clear Quartz.
Uruguay
Known for high-quality, deep purple Amethyst.
Madagascar
Produces significant quantities of Amethyst, Smoky Quartz, and Clear Quartz.
United States
Various localities for Clear Quartz (e.g., Arkansas), Smoky Quartz (e.g., Colorado), and Amethyst (e.g., North Carolina, Arizona).
Switzerland
Historically known for fine Smoky Quartz.
India
Source of various chalcedony forms, including onyx.
Mexico
Produces Amethyst and other quartz varieties.
Collecting tips
- Hardness Test. All quartz varieties have a Mohs hardness of 7, which can scratch glass. This helps differentiate them from softer minerals.
- Specific Gravity. Quartz has a specific gravity of 2.65. This can be used to distinguish it from denser or lighter materials if precise measurements are possible.
- Absence of Cleavage. The lack of cleavage and presence of conchoidal fracture are key identifiers for quartz.
- Color and Transparency. Observe the characteristic colors and transparency: purple for amethyst, smoky gray/brown for smoky quartz, colorless and transparent for clear quartz, and opaque black for black onyx.
- Banding (for Onyx). While black onyx is typically uniform, some natural onyx may show very subtle parallel banding upon close inspection, distinguishing it from other black minerals like obsidian (which is volcanic glass).
Quick Check
- Color:
- Amethyst: purple; Smoky Quartz: gray/brown; Clear Quartz: colorless; Black Onyx: black
- Luster:
- Vitreous (glassy)
- Streak:
- White (for all varieties)
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