Gonyerite is an extremely rare member of the chlorite group, typically found as platy, micaceous crystals in manganese-rich metamorphic environments. It is most famous for its occurrences in the Långban mines of Sweden and is highly sought after by collectors of manganese minerals.

Hardness

2.5

Mohs

Luster

Pearly

Streak

Chocolate brown

Transparency

Translucent

mineralrareChlorite Group family

Gonyerite

Hardness: 2.5
Luster: Pearly
Streak: Chocolate brown
Transparency: Translucent

Is this gonyerite?

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 gonyerite with a known reference. Gonyerite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: chocolate brown.
3
Read the luster
Hold the specimen under a strong light. Luster: pearly.
4
Match the color range
Compare against the expected color range: dark brown, brownish black, bright green.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: platy, radial.

Often confused with

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

mineral

Clinochlore

Mohs 2-2.5

How to tell apart: Streak differs, so Gonyerite leaves chocolate brown, Clinochlore leaves greenish white to white.

How to tell apart: Streak differs, so Gonyerite leaves chocolate brown, Chamosite leaves green to gray.

Compare →

Often found alongside gonyerite

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

All properties

Chemical formula: Mn₅Fe(Si₃FeO₁₀)(OH)₈
Mohs hardness: 2.5
Density: 3.01 g/cm³
Colors: Dark brown Brownish black Bright green
Streak: Chocolate brown
Luster: Pearly
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Platy, radial
Cleavage: {001}, perfect
Rarity: Rare
Uses: Collector
Host rock: In hydrothermal veinlets cutting skarn (Långban, Sweden)

Where rockhounds find gonyerite

Classic worldwide localities

Långban, and at the Harstigen mine, near Persberg, Värmland, Sweden
Wessels mine, near Kuruman, Cape Province, South Africa

Field-hunting tip

Where it forms: In hydrothermal veinlets cutting skarn (Långban, Sweden). If you start seeing caryopilite, bementite, berzeliite in float, you are in the right ground. Typical habit: platy, radial. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify gonyerite?+

Mohs hardness is 2.5. Luster: pearly. The streak is chocolate brown. Common colors include dark brown, brownish black, bright green.

Where is gonyerite found?+

Notable localities include Långban, and at the Harstigen mine, near Persberg, Värmland, Sweden; Wessels mine, near Kuruman, Cape Province, South Africa.

What rocks look like gonyerite?+

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

What minerals are found with gonyerite?+

Gonyerite commonly co-occurs with Caryopilite, Bementite, Berzeliite, Barite, Garnet. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does gonyerite form in?+

Where it forms: In hydrothermal veinlets cutting skarn (Långban, Sweden). Working float back to the host body is the standard way to chase a fresh occurrence.

What is gonyerite used for?+

Gonyerite is used in collector.

Find gonyerite on the map

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