Pennantite is a manganese-rich member of the chlorite group that typically forms as soft, micaceous plates. Collectors prize it for its distinct brown to orange-brown color, which differentiates it from the common green iron-magnesium chlorites. It is most frequently found in metamorphosed manganese deposits where it occurs alongside minerals like hausmannite.

Hardness

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineralrareChlorite Group family

Pennantite

Hardness: 2
Luster: Pearly
Streak: White
Transparency: Translucent

Is this pennantite?

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 pennantite with a known reference. Pennantite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Pennantite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Pennantite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: brown, reddish-brown, orange-brown.
5
Look at form & habit
Crystal system: triclinic. Typical habit: platy crystals, foliated masses, hexagonal-shaped plates.

Often confused with

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

How to tell apart: Chamosite is the harder of the two (Mohs 3 vs. 2); streak differs — Pennantite leaves white, Chamosite leaves white to pale green.

Often found alongside pennantite

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

All properties

Chemical formula: (Mn,Al)₆(Si,Al)₄O₁₀(OH)₈
Mohs hardness: 2
Density: 3.0-3.1 g/cm³
Colors: Brown Reddish-brown Orange-brown
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Triclinic
Crystal habit: Platy Crystals, Foliated Masses, Hexagonal-shaped Plates
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Manganese-rich Hydrothermal Deposits
Typical price: $20-150 per specimen depending on size and crystal definition

Where rockhounds find pennantite

Classic worldwide localities

Gwenlais Quarry, Wales
Franklin, New Jersey, USA
Langban, Sweden

Field-hunting tip

Look in manganese-rich hydrothermal deposits country — that is the host setting where pennantite typically forms. If you start seeing quartz, calcite, hausmannite in float, you are in the right ground. Field specimens usually show a platy crystals, foliated masses, hexagonal-shaped plates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify pennantite?+

Mohs hardness is 2. It typically shows a pearly luster. The streak is white. Common colors include brown, reddish-brown, orange-brown.

Where is pennantite found?+

Notable localities include Gwenlais Quarry, Wales; Franklin, New Jersey, USA; Langban, Sweden.

How much is pennantite worth?+

Typical asking prices fall in the range of $20-150 per specimen depending on size and crystal definition. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like pennantite?+

Pennantite is most often confused with Clinochlore, Chamosite, Cookeite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with pennantite?+

Pennantite commonly co-occurs with Quartz, Calcite, Hausmannite, Barite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does pennantite form in?+

Pennantite typically forms in manganese-rich hydrothermal deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is pennantite used for?+

Pennantite is used in collector.

Find pennantite on the map

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