mineral
Milky Quartz Geode/Nodule
Crystalline Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Milky white with iron-oxide (rust) staining; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Milky white with iron-oxide (rust) staining
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Milky white with iron-oxide (rust) staining; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed in cavities within volcanic or sedimentary rocks through the precipitation of silica from hydrothermal solutions or groundwater. This specimen shows a botryoidal or nodular exterior with a crystalline quartz core.
Uses & applications
Commonly used as a decorative specimen, in lapidary work (tumbling), and historically used in glassmaking or as a source of silicon for electronics.
Geological facts
Quartz is the second most abundant mineral in Earth's continental crust. Specimens like this one, with orange-brown staining, get their color from limonite or hematite impurities.
Field identification & locations
Identify by its hardness (can scratch glass), lack of cleavage, and white-to-clear color. Commonly found in gravel pits, stream beds, and weathering out of limestone or basalt.
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Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Sandstone with Mineral Veining or Crust
Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
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Mineral
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