Ferro-glaucophane is a relatively rare sodic amphibole that acts as an indicator mineral for high-pressure, low-temperature metamorphism. It typically forms prismatic to fibrous crystals in blueschist rocks and is distinguished from common glaucophane by its iron-rich composition. Collectors generally find these in dense, foliated metamorphic assemblages.
Is this ferro-glaucophane?
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 ferro-glaucophane with a known reference. Ferro-glaucophane sits at Mohs 6-6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferro-glaucophane leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ferro-glaucophane typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, blue-black, lavender.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, fibrous, massive.
Often confused with
Ferro-glaucophane vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside ferro-glaucophane
Minerals reported to co-occur with ferro-glaucophane. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- □{Na₂}{Fe²⁺₃Al₂}(Si₈O₂₂)(OH)₂
- Mohs hardness
- 6-6.5
- Density
- 3.1-3.2 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Fibrous, Massive
- Cleavage
- Perfect On {110}
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Blueschist Facies Metamorphic Rocks
- Typical price
- $20-100 for specimens
Where rockhounds find ferro-glaucophane
Classic worldwide localities
- California, USA
- Japan
- Italy
- Greece
- Russia
Field-hunting tip
Look in blueschist facies metamorphic rocks country — that is the host setting where ferro-glaucophane typically forms. If you start seeing lawsonite, jadeite, chlorite in float, you are in the right ground. Field specimens usually show a prismatic crystals, fibrous, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferro-glaucophane?+
Where is ferro-glaucophane found?+
How much is ferro-glaucophane worth?+
What rocks look like ferro-glaucophane?+
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Find ferro-glaucophane on the map
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