Rondorfite is a very rare silicate mineral found in xenoliths within volcanic ejecta. It typically occurs as small, orange-brown to amber dodecahedral crystals and is known primarily from the Bellerberg Volcano in the Eifel region of Germany.
Is this rondorfite?
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 rondorfite with a known reference. Rondorfite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light amber.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: orange brown, amber brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: anhedral grains.
Often confused with
Rondorfite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside rondorfite
Minerals reported to co-occur with rondorfite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₈Mg(SiO₄)₄Cl₂
- Mohs hardness
- 6
- Density
- 3.03 g/cm³
- Colors
- Orange brownAmber brown
- Streak
- Light amber
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Cubic
- Crystal habit
- Anhedral grains
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In metasomatized limestone xenoliths in leucite tephrite lava or ignimibrites
Where rockhounds find rondorfite
Classic worldwide localities
- A quarry at the Bellerberg volcano lava field, near Ettringen, 2 km north of Mayen, Laacher See region, eastern Eifel area, Germany
- Upper Chegem Caldera, Northern Caucasus, Kabardino-Balkaria, Russia
- Zastávka, Rosice-Oslavany Coalfield, Czech Republic
Field-hunting tip
Where it forms: In metasomatized limestone xenoliths in leucite tephrite lava or ignimibrites. If you start seeing ettringite-thaumasite, mayenite, ternesite in float, you are in the right ground. Typical habit: anhedral grains. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rondorfite?+
Where is rondorfite found?+
What rocks look like rondorfite?+
What minerals are found with rondorfite?+
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What is rondorfite used for?+
Find rondorfite on the map
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