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, 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.