metamorphic
Dendritic Agate or Spotted Quartzite
Silicon Dioxide (SiO2) with inclusions
Hardness: 7 (Mohs scale); Color: White, grey, or bluish with black/dark inclusions; Luster: Vitreous to waxy; Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65
- Hardness
- 7 (Mohs scale)
- Color
- White, grey, or bluish with black/dark inclusions
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: White, grey, or bluish with black/dark inclusions; Luster: Vitreous to waxy; Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65
Formation & geological history
Formed from the recrystallization of quartz-rich sandstone through heat and pressure (Metamorphism), or as secondary silica fillings in rock cavities. Dark markings are often manganese or iron oxide inclusions.
Uses & applications
Commonly used as decorative stones, landscaping 'river rocks', tumbled pocket stones, or in costume jewelry and beadwork.
Geological facts
The black 'mossy' or 'spotted' patterns are known as dendrites, which branch out like trees, though in this specimen they appear as more rounded spots or patches within the quartz matrix.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and grainy but fused texture. Often found in riverbeds or as glacial till in varied geological environments.
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