Slate is a fine-grained, foliated metamorphic rock that is created by the low-grade metamorphism of shale or mudstone. It is easily identified by its characteristic slaty cleavage, which allows the rock to be split into thin, flat, and durable sheets.

Hardness

2.5-4

Mohs

Luster

Dull

Transparency

Opaque

metamorphiccommon

Slate

Hardness: 2.5-4
Luster: Dull
Transparency: Opaque

Is this slate?

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 slate with a known reference. Slate sits at Mohs 2.5-4, softer than the next harder reference, harder than the previous one.
2
Read the texture
Look at a fresh break with a hand lens. Texture: Foliated with slaty cleavage; splits into thin, flat sheets. Grain size: The finest-grained foliated metamorphic rock; crystals are microscopic.
3
Pick out the minerals
Composition: Low-grade metamorphosed shale-type rock of clay or volcanic ash. Identify the two or three most abundant grains.
4
Read the luster
Hold the specimen under a strong light. Luster: dull.
5
Match the color range
Compare against the expected color range: gray, black, green, red, purple, brown.

Often confused with

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

How to tell apart: Luster reads dull on Slate and silky on Phyllite.

How to tell apart: Luster reads dull on Slate and pearly on Schist.

Compare →

Often found alongside slate

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

All properties

Mohs hardness: 2.5-4
Density: 2.7-2.9 g/cm³
Colors: Gray Black Green Red Purple Brown
Luster: Dull
Transparency: Opaque
Rarity: Common
Uses: Construction, Roofing, Flooring, Decorative
Host rock: low-grade regional metamorphism of shale or mudstone
Texture: Foliated with slaty cleavage; splits into thin, flat sheets
Grain size: The finest-grained foliated metamorphic rock; crystals are microscopic
Composition: Low-grade metamorphosed shale-type rock of clay or volcanic ash

Where rockhounds find slate

Classic worldwide localities

Wales
Pennsylvania, USA
France
Germany
Spain

Field-hunting tip

Where it forms: low-grade regional metamorphism of shale or mudstone. If you start seeing quartz, muscovite, chlorite in float, you are in the right ground.

Common questions

How do you identify slate?+

Mohs hardness is 2.5-4. Texture: Foliated with slaty cleavage; splits into thin, flat sheets. Composition: Low-grade metamorphosed shale-type rock of clay or volcanic ash. Luster: dull. Common colors include gray, black, green, red.

Where is slate found?+

Notable localities include Wales; Pennsylvania, USA; France; Germany; Spain.

What rocks look like slate?+

Slate is most often confused with Shale, Phyllite, Schist. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with slate?+

Slate commonly co-occurs with Quartz, Muscovite, Chlorite, Hematite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does slate form in?+

Where it forms: low-grade regional metamorphism of shale or mudstone. Working float back to the host body is the standard way to chase a fresh occurrence.

What is slate used for?+

Slate is used in construction, roofing, flooring, decorative.

Find slate on the map

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