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, so Rhönite leaves brownish grey, Aenigmatite leaves reddish-brown.

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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, 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.