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, 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.