Gray agate is a microcrystalline variety of quartz characterized by subtle, often concentric banding in shades of gray, white, and sometimes black. It is commonly found as nodules or fillings in volcanic cavities and is a favorite among lapidaries for its toughness and polishability. Look for distinctive waxy luster and translucent banding when identifying hand specimens.
Is this gray agate?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch gray agate with a known reference. Gray Agate sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: waxy.
- 4Match the color rangeCompare against the expected color range: gray, gray, white, black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: banded, nodular, massive.
Often confused with
Gray Agate vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside gray agate
Minerals reported to co-occur with gray agate. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.58-2.64 g/cm³
- Streak
- White
- Luster
- Waxy
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Banded, nodular, massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- volcanic cavities, sedimentary vugs, hydrothermal veins
Where rockhounds find gray agate
1 mapped spotsClassic worldwide localities
- Botswana
- Brazil
- Uruguay
- USA
- India
Field-hunting tip
Where it forms: volcanic cavities, sedimentary vugs, hydrothermal veins. If you start seeing quartz, calcite, zeolites in float, you are in the right ground. Typical habit: banded, nodular, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri. Start trip planning there.
More gray agate photos
Common questions
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Find gray agate on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
