mineral
Agate / Chalcedony (Rough Nodule)
Microcrystalline Quartz (Silicon Dioxide, SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 on the Mohs scale; Color: Amber-brown, translucent yellow, white, and earthy tan; Luster: Waxy to vitreous; Fracture: Conchoidal; Crystal System: Trigonal (microcrystalline/cryptocrystalline aggregate); Specific Gravity: ~2.58-2.64.
- Hardness
- 6
- Color
- Amber-brown, translucent yellow, white, and earthy tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on the Mohs scale; Color: Amber-brown, translucent yellow, white, and earthy tan; Luster: Waxy to vitreous; Fracture: Conchoidal; Crystal System: Trigonal (microcrystalline/cryptocrystalline aggregate); Specific Gravity: ~2.58-2.64.
Formation & geological history
Formed as secondary deposits within cavities (vesicles) of volcanic igneous rocks or sedimentary strata where silica-rich groundwater precipitated microcrystalline quartz over long periods.
Uses & applications
Commonly collected as rough specimens, tumbled, sliced, or cabbed for lapidary arts and jewelry, or kept by mineral enthusiasts.
Geological facts
Rough weathered agates often exhibit pitted, irregular exterior 'skins' or rinds known as cortex, frequently showing subtle translucency when backlit or wet.
Field identification & locations
Identified in the field by its waxy luster, high hardness (scratches glass, cannot be scratched by steel), conchoidal fracture, and characteristic translucency in broken or thinned edges. Frequently found in river gravels, volcanic regions, and glacial deposits.
