Hornfels is a fine-grained, hard, non-foliated metamorphic rock created through contact metamorphism where heat from igneous intrusions bakes the surrounding country rock. It typically appears as a dull, dense, and tough stone with a splintery fracture, often displaying small visible crystals like andalusite or cordierite that grew during the heating process.

Hardness

5-7

Mohs

Luster

Dull

Streak

White

Transparency

Opaque

metamorphiccommon

Hornfels

Hardness: 5-7
Luster: Dull
Streak: White
Transparency: Opaque

Is this hornfels?

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

Often confused with

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

How to tell apart: Hornfels is noticeably harder (Mohs 5-7 vs. 2-3).

How to tell apart: Hornfels is noticeably harder (Mohs 5-7 vs. 3-4).

Compare →

Often found alongside hornfels

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

All properties

Mohs hardness: 5-7
Density: 2.6-3.0 g/cm³
Colors: Gray Dark Gray Black Brown Greenish
Streak: White
Luster: Dull
Transparency: Opaque
Crystal habit: Massive
Cleavage: None
Rarity: Common
Uses: Educational, Collector, Construction
Host rock: Contact Metamorphic Zones
Typical price: $5-20 per specimen

Where rockhounds find hornfels

1 mapped spots

Classic worldwide localities

United Kingdom
Germany
United States
France

Field-hunting tip

Look in contact metamorphic zones country — that is the host setting where hornfels typically forms. If you start seeing andalusite, cordierite, biotite 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. In the U.S., the densest reported localities are in New Jersey — start trip planning there.

Browse 1 U.S. spots for hornfels →

Common questions

How do you identify hornfels?+

Mohs hardness is 5-7. It typically shows a dull luster. The streak is white. Common colors include gray, dark gray, black, brown.

Where is hornfels found?+

Notable localities include United Kingdom; Germany; United States; France.

Can I find hornfels in the United States?+

RockHoundR maps 1 hornfels rockhounding spots across 1 U.S. states — the top states are New Jersey.

How much is hornfels worth?+

Typical asking prices fall in the range of $5-20 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like hornfels?+

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

What minerals are found with hornfels?+

Hornfels commonly co-occurs with andalusite, cordierite, biotite, quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hornfels form in?+

Hornfels typically forms in contact metamorphic zones. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hornfels used for?+

Hornfels is used in educational, collector, construction.

Find hornfels on the map

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