Greywacke is a texturally immature, poorly sorted sandstone characterized by its dark color and high proportion of lithic fragments and rock grains. Collectors often find it in mountainous regions where deep-water marine sequences have been tectonically uplifted and exposed. It is easily identified by its gritty feel and lack of distinct bedding compared to typical sedimentary rocks.

Hardness

6-7

Mohs

Luster

Dull

Streak

White

Transparency

Opaque

sedimentarycommon

Greywacke

Hardness: 6-7
Luster: Dull
Streak: White
Transparency: Opaque

Is this greywacke?

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 greywacke with a known reference. Greywacke sits at Mohs 6-7 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Greywacke leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Greywacke typically shows a dull luster.
4
Match the color range
Compare against the expected color range: gray, dark gray, brownish gray.
5
Look at form & habit
Typical habit: massive.

Often confused with

Greywacke vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside greywacke

Minerals reported to co-occur with greywacke. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Mohs hardness: 6-7
Density: 2.6-2.7 g/cm³
Colors: Gray Dark Gray Brownish Gray
Streak: White
Luster: Dull
Transparency: Opaque
Crystal habit: Massive
Cleavage: None
Rarity: Common
Uses: Construction Aggregate, Decorative Stone, Educational
Host rock: Marine Sedimentary Basins
Typical price: $1-10 per specimen

Where rockhounds find greywacke

Classic worldwide localities

New Zealand
Scotland
Wales
California, USA

Field-hunting tip

Look in marine sedimentary basins country — that is the host setting where greywacke typically forms. If you start seeing quartz, feldspar, mica in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify greywacke?+

Mohs hardness is 6-7. It typically shows a dull luster. The streak is white. Common colors include gray, dark gray, brownish gray.

Where is greywacke found?+

Notable localities include New Zealand; Scotland; Wales; California, USA.

How much is greywacke worth?+

Typical asking prices fall in the range of $1-10 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like greywacke?+

Greywacke is most often confused with Sandstone, Basalt. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with greywacke?+

Greywacke commonly co-occurs with Quartz, Feldspar, Mica, Chlorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does greywacke form in?+

Greywacke typically forms in marine sedimentary basins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is greywacke used for?+

Greywacke is used in construction aggregate, decorative stone, educational.

Find greywacke on the map

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