mineral
Amethyst Sage Agate
Silicon Dioxide (SiO2) with trace minerals (Manganese/Iron oxides)
Hardness: 6.5-7 on the Mohs scale; Color: Lavender, deep purple, or gray with black branching (dendritic) manganese inclusions; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64
- Hardness
- 6
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on the Mohs scale; Color: Lavender, deep purple, or gray with black branching (dendritic) manganese inclusions; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64
Formation & geological history
Formed as a chemical precipitate in cavities within volcanic host rocks. Soluble silica-rich fluids permeate the rock, depositing layers of chalcedony over millions of years. This specific variety is found primarily in the Bilk Creek Mountains area of Northern Nevada, USA, dating back to the Miocene epoch.
Uses & applications
Used extensively by lapidary artists for cabochons, pendants, and jewelry sets. It is highly valued by collectors for its unique 'scenic' or dendritic patterns that resemble trees or desert sagebrush.
Geological facts
Despite the name 'Amethyst,' it is technically a chalcedony/agate and not a macro-crystalline amethyst quartz. The name comes from the characteristic lavender color. The black 'branches' seen in the stone are actually manganese dendrites that resemble organic plant life but are entirely mineral-based.
Field identification & locations
Can be identified in the field as translucent to semi-opaque nodules or fill in volcanic rock. To distinguish it, collectors look for the distinctive combination of lavender background color with 'dendrites' (black moss-like splotches). It is primarily found in the Denio area of the Oregon/Nevada border.
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