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.
Is this rhönite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch rhönite with a known reference. Rhönite sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brownish gray.
- 3Read the lusterHold the specimen under a strong light. Luster: semimetallic.
- 4Match the color rangeCompare against the expected color range: brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: prismatic, skeletal, tabular.
Often confused with
Rhönite vs. its common look-alikes, and how to tell them apart in the field.
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
- Ca₄(Mg₈Fe₂Ti₂)O₄[Si₆Al₆O₃₆]
- Mohs hardness
- 5-6
- Density
- 3.4-3.76 g/cm³
- Colors
- Streak
- Brownish gray
- Luster
- Semimetallic
- Transparency
- Translucent to opaque
- Crystal system
- Triclinic
- Crystal habit
- Prismatic, skeletal, tabular
- Cleavage
- {010}, {001}, good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In silica-undersaturated, alkalic, mafic to intermediate igneous rocks, as a primary mineral or an alteration product of amphiboles
Where rockhounds find rhönite
Classic worldwide localities
- Found near Study Butte, Brewster Co., Texas, and north of Kalaheo, Kauai, Hawaii, USA
- Rhön Mountains, at Scharnhausen, near Stuttgart, Hesse, Germany
- Eichersattel, Sattelberg, Germany
- Löbauer Berg, Saxony, Germany
- Skåne, Sweden
- Puy de Saint-Sandoux, Auvergne, France
Field-hunting tip
Where it forms: In silica-undersaturated, alkalic, mafic to intermediate igneous rocks, as a primary mineral or an alteration product of amphiboles. If you start seeing titanian augite, kaersutite, alkalic feldspar in float, you are in the right ground. Typical habit: prismatic, skeletal, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rhönite?+
Where is rhönite found?+
What rocks look like rhönite?+
What minerals are found with rhönite?+
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Find rhönite on the map
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