A quartz concretion is a rounded, compact mass of silica that forms within a sedimentary layer such as limestone or shale. It appears as an unremarkable rounded rock which, when broken open, may reveal a solid, banded, or drusy interior.
Is this quartz concretion?
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 quartz concretion with a known reference. Quartz Concretion sits at Mohs 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: dull to waxy.
- 4Match the color rangeCompare against the expected color range: white, gray, brown, tan.
- 5Look at form & habitCrystal system: trigonal. Typical habit: nodular, spherical, or concretionary masses.
Often confused with
Quartz Concretion vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside quartz concretion
Minerals reported to co-occur with quartz concretion. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 7
- Density
- 2.65 g/cm³
- Streak
- White
- Luster
- Dull to waxy
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Nodular, spherical, or concretionary masses
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Lapidary
- Host rock
- sedimentary rock environments
Where rockhounds find quartz concretion
2 mapped spotsClassic worldwide localities
- Missouri, USA
- Arkansas, USA
- South Dakota, USA
- France
- Germany
Field-hunting tip
Where it forms: sedimentary rock environments. If you start seeing calcite, dolomite, pyrite in float, you are in the right ground. Typical habit: nodular, spherical, or concretionary masses. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Kansas, Nebraska. Start trip planning there.
More quartz concretion photos
Common questions
How do you identify quartz concretion?+
Where is quartz concretion found?+
Can I find quartz concretion in the United States?+
What rocks look like quartz concretion?+
What minerals are found with quartz concretion?+
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Find quartz concretion on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
