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.

Hardness

Mohs

Luster

Dull to Waxy

Streak

White

Transparency

Opaque

mineralcommonQuartz family

Quartz Concretion

Hardness: 7
Luster: Dull to Waxy
Streak: White
Transparency: Opaque

No image

Is this quartz concretion?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try 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.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Quartz Concretion leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Quartz Concretion typically shows a dull to waxy luster.
4
Match the color range
Compare against the expected color range: white, gray, brown, tan.
5
Look at form & habit
Crystal 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.

mineral

Flint Nodule

Mohs 7

How to tell apart: Luster reads dull to waxy on Quartz Concretion and waxy on Flint Nodule.

How to tell apart: Luster reads dull to waxy on Quartz Concretion and waxy on Flint.

Compare →

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
Colors: White Gray Brown Tan
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 spots

Classic worldwide localities

Missouri, USA
Arkansas, USA
South Dakota, USA
France
Germany

Field-hunting tip

Look in sedimentary rock environments country, the host setting where quartz concretion typically forms. If you start seeing calcite, dolomite, pyrite in float, you are in the right ground. Field specimens usually show a nodular, spherical, or concretionary masses habit, so 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.

Browse 2 U.S. spots for quartz concretion →

Common questions

How do you identify quartz concretion?+

Mohs hardness is 7. It typically shows a dull to waxy luster. The streak is white. Common colors include white, gray, brown, tan.

Where is quartz concretion found?+

Notable localities include Missouri, USA; Arkansas, USA; South Dakota, USA; France; Germany.

Can I find quartz concretion in the United States?+

RockHoundR maps 2 quartz concretion rockhounding spots across 2 U.S. states. The top states are Kansas, Nebraska.

What rocks look like quartz concretion?+

Quartz Concretion is most often confused with Flint Nodule, Flint. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with quartz concretion?+

Quartz Concretion commonly co-occurs with Calcite, Dolomite, Pyrite, Goethite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does quartz concretion form in?+

Quartz Concretion typically forms in sedimentary rock environments. Working float back to the host body is the standard way to chase a fresh occurrence.

What is quartz concretion used for?+

Quartz Concretion is used in collector, lapidary.

Find quartz concretion on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.