Ferro-actinolite is an iron-rich member of the amphibole group found primarily in metamorphosed iron-rich sedimentary rocks. It often occurs as dark green to black elongated prismatic crystals or in radiating fibrous masses, which require careful handling due to potential asbestiform characteristics.
Is this ferro-actinolite?
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-actinolite with a known reference. Ferro-actinolite sits at Mohs 5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferro-actinolite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ferro-actinolite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark green, black, brownish-green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, acicular, fibrous.
Often confused with
Ferro-actinolite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside ferro-actinolite
Minerals reported to co-occur with ferro-actinolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂(Fe²⁺)₅Si₈O₂₂(OH)₂
- Mohs hardness
- 5-6
- Density
- 3.4-3.5 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Acicular, Fibrous
- Cleavage
- Perfect in Two Directions
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Metamorphic Rocks
- Typical price
- $15-80 thumbnail, $50-250 cabinet
Where rockhounds find ferro-actinolite
Classic worldwide localities
- Sweden
- USA
- Japan
- Russia
- Canada
Field-hunting tip
Look in metamorphic rocks country — that is the host setting where ferro-actinolite typically forms. If you start seeing magnetite, quartz, calcite in float, you are in the right ground. Field specimens usually show a prismatic crystals, acicular, fibrous habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferro-actinolite?+
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Is ferro-actinolite safe to handle?+
What rocks look like ferro-actinolite?+
What minerals are found with ferro-actinolite?+
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Find ferro-actinolite on the map
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