Rhönite is a relatively rare member of the aenigmatite group typically found in silica-undersaturated alkalic volcanic rocks. It forms dark, brownish-black tabular or prismatic crystals and is primarily a curiosity for advanced mineral collectors studying volcanic paragenesis.

Hardness

5.5-6

Mohs

Luster

Vitreous

Streak

Brownish Grey

Transparency

Opaque

mineralrareAenigmatite Group family

Rhönite

Hardness: 5.5-6
Luster: Vitreous
Streak: Brownish Grey
Transparency: Opaque

Is this rhönite?

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 rhönite with a known reference. Rhönite sits at Mohs 5.5-6 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Rhönite leaves a brownish grey streak.
3
Read the luster
Hold the specimen under a strong light. Rhönite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: black, brown, dark brown.
5
Look at form & habit
Crystal system: triclinic. Typical habit: tabular crystals, granular aggregates, prismatic.

Often confused with

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

mineral

Aenigmatite

Mohs 5.5-6

How to tell apart: Streak differs — Rhönite leaves brownish grey, Aenigmatite leaves reddish-brown.

Compare →

Often found alongside rhönite

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

All properties

Chemical formula: (Ca,Na,Mg,Fe²⁺,Fe³⁺,Ti,Al)₈(Si,Al)₆O₂₀
Mohs hardness: 5.5-6
Density: 3.5-3.6 g/cm³
Colors: Black Brown Dark Brown
Streak: Brownish Grey
Luster: Vitreous
Transparency: Opaque
Crystal system: Triclinic
Crystal habit: Tabular Crystals, Granular Aggregates, Prismatic
Cleavage: Good in Two Directions
Rarity: Rare
Uses: Collector
Host rock: Alkalic Igneous Rocks, Basaltic Lavas
Typical price: $20-150 per specimen depending on size and crystal quality

Where rockhounds find rhönite

Classic worldwide localities

Rhön Mountains, Germany
Etna, Italy
Kaiserstuhl, Germany
Cape Verde
Hocheifel, Germany

Field-hunting tip

Look in alkalic igneous rocks, basaltic lavas country — that is the host setting where rhönite typically forms. If you start seeing nepheline, olivine, augite in float, you are in the right ground. Field specimens usually show a tabular crystals, granular aggregates, prismatic habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify rhönite?+

Mohs hardness is 5.5-6. It typically shows a vitreous luster. The streak is brownish grey. Common colors include black, brown, dark brown.

Where is rhönite found?+

Notable localities include Rhön Mountains, Germany; Etna, Italy; Kaiserstuhl, Germany; Cape Verde; Hocheifel, Germany.

How much is rhönite worth?+

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

What rocks look like rhönite?+

Rhönite is most often confused with Aenigmatite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with rhönite?+

Rhönite commonly co-occurs with Nepheline, Olivine, Augite, Magnetite, Leucite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does rhönite form in?+

Rhönite typically forms in alkalic igneous rocks, basaltic lavas. Working float back to the host body is the standard way to chase a fresh occurrence.

What is rhönite used for?+

Rhönite is used in collector.

Find rhönite on the map

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