Agate
What is Agate?
Agate is a cryptocrystalline form of silica, essentially chalcedony exhibiting a fine grain and vibrant color variations. Agates are primarily formed within volcanic and metamorphic rocks. The unique banding and patterns are a result of the gradual deposition of silica-rich fluids within cavities. These cavities can be of various shapes and sizes, leading to the diverse appearances of agate. The different colors and patterns are due to the presence of various impurities.
Optical Properties
- Refractive Index
- 1.530-1.540
- Pleochroism
- None
- Optical Character
- Uniaxial positive
- Dispersion
- 0.013
Discover Values
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Agate before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Where to Find Agate
RockHoundR, the free-to-download rockhounding map from the Ruby Glint team, shows where collectors find agate in the US, with land-access notes for BLM land and national forests. Collecting is banned in national parks.
See where to find agateAlways check the local rules and get the landowner's permission before you collect.
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Quick Facts
Physical Properties
- Color
- White, gray, blue, red, orange, yellow, green, brown, black, pink, purple
- Hardness (Mohs)
- 6.5-7
- Rock tumbling
- Tumbles well
- Density
- 2.58-2.64 g/cm³
- Streak
- White
- Luster
- Vitreous
- Crystal System
- Hexagonal
Chemical Properties
- Chemical Formula
- SiO2
- Elements
- Si, O
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Agate FAQs
How do I identify Agate?
Agate can be identified by its hardness of 6.5-7 on the Mohs scale, White color, Vitreous luster, Hexagonal crystal system. Look for these key characteristics when examining specimens.
What color is Agate?
Agate typically appears in White, gray, blue, red, orange, yellow, green, brown, black, pink, purple. Color can vary depending on impurities and formation conditions.
How hard is Agate?
Agate has a hardness of 6.5-7 on the Mohs scale. This gives it moderate hardness.