Ferro-anthophyllite is an iron-rich member of the amphibole group typically found in medium-to-high grade metamorphic rocks. It is easily identified by its fibrous or bladed habit and brownish color, though it is often difficult to distinguish from other amphiboles without chemical analysis.
Is this ferro-anthophyllite?
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-anthophyllite with a known reference. Ferro-anthophyllite sits at Mohs 5.5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferro-anthophyllite leaves a white to gray streak.
- 3Read the lusterHold the specimen under a strong light. Ferro-anthophyllite typically shows a vitreous to silky luster.
- 4Match the color rangeCompare against the expected color range: brown, greenish-brown, dark gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, acicular, or radiating aggregates.
Often confused with
Ferro-anthophyllite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ferro-anthophyllite leaves white to gray, Cummingtonite leaves white; luster reads vitreous to silky on Ferro-anthophyllite and vitreous on Cummingtonite.
How to tell apart: Streak differs — Ferro-anthophyllite leaves white to gray, Anthophyllite leaves white; luster reads vitreous to silky on Ferro-anthophyllite and vitreous on Anthophyllite.
How to tell apart: Streak differs — Ferro-anthophyllite leaves white to gray, Actinolite leaves white.
Often found alongside ferro-anthophyllite
Minerals reported to co-occur with ferro-anthophyllite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe²⁺₇Si₈O₂₂(OH)₂
- Mohs hardness
- 5.5-6
- Density
- 3.3-3.5 g/cm³
- Streak
- White to Gray
- Luster
- Vitreous to Silky
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Acicular, Or Radiating Aggregates
- Cleavage
- Perfect Prismatic On {110}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Metamorphic Rocks
- Typical price
- $10-50 per specimen
Where rockhounds find ferro-anthophyllite
Classic worldwide localities
- Finland
- USA
- Sweden
- Canada
Field-hunting tip
Look in metamorphic rocks country — that is the host setting where ferro-anthophyllite typically forms. If you start seeing garnet, cordierite, staurolite in float, you are in the right ground. Field specimens usually show a fibrous, acicular, or radiating aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferro-anthophyllite?+
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Find ferro-anthophyllite on the map
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