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. Gray Agate leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Gray Agate typically shows a waxy luster.
- 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
- Typical price
- $5-50 for small specimens, $20-200 for polished slabs
Where rockhounds find gray agate
1 mapped spotsClassic worldwide localities
- Botswana
- Brazil
- Uruguay
- USA
- India
Field-hunting tip
Look in volcanic cavities, sedimentary vugs, hydrothermal veins country — that is the host setting where gray agate typically forms. If you start seeing quartz, calcite, zeolites in float, you are in the right ground. Field specimens usually show a banded, nodular, massive habit, so 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.
Common questions
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Find gray agate on the map
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