Ferroindialite is a rare hexagonal member of the indialite-cordierite series, distinguished by its high iron content. It is typically found in high-temperature, low-pressure pyrometamorphic environments where it forms small, prism-shaped crystals. It is nearly indistinguishable from ordinary cordierite without advanced X-ray diffraction or chemical analysis.
Is this ferroindialite?
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 ferroindialite with a known reference. Ferroindialite sits at Mohs 7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: brownish purple, gray with a violet-blue tint.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: hexagonal prisms, massive.
Often confused with
Ferroindialite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside ferroindialite
Minerals reported to co-occur with ferroindialite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂Al₃(Si₅AlO₁₈)
- Mohs hardness
- 7
- Density
- 2.66 g/cm³
- Colors
- Brownish purpleGray with a violet-blue tint
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Hexagonal
- Crystal habit
- Hexagonal prisms, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a metamorphosed pelitic xenolith in alkaline basalt
Where rockhounds find ferroindialite
Classic worldwide localities
- Caspar quarry, Bellerberg Mountain, near Mayen, Eifel region, Rheinland-Pfalz, Germany
Field-hunting tip
Where it forms: In a metamorphosed pelitic xenolith in alkaline basalt. If you start seeing sillimanite, sanidine, phlogopite in float, you are in the right ground. Typical habit: hexagonal prisms, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferroindialite?+
Where is ferroindialite found?+
What rocks look like ferroindialite?+
What minerals are found with ferroindialite?+
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What is ferroindialite used for?+
Find ferroindialite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
