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 7-7.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferroindialite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ferroindialite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, colorless, gray.
- 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
- (Mg,Fe)₂Al₄Si₅O₁₈
- Mohs hardness
- 7-7.5
- Density
- 2.6-2.7 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Hexagonal
- Crystal habit
- Hexagonal Prisms, Massive
- Cleavage
- Poor On {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Pyrometamorphic Rocks
- Typical price
- $50-300 per specimen
Where rockhounds find ferroindialite
Classic worldwide localities
- Bocche di Bonifacio, Sardinia
- various pyrometamorphic complexes
Field-hunting tip
Look in pyrometamorphic rocks country — that is the host setting where ferroindialite typically forms. If you start seeing quartz, feldspar, mullite in float, you are in the right ground. Field specimens usually show a hexagonal prisms, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferroindialite?+
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Find ferroindialite on the map
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