Actinolite is a common metamorphic amphibole mineral often found in greenschist facies rocks and contact metamorphic zones. Collectors often seek out its distinctive radiating, acicular, or prismatic crystal clusters, though it can also appear in massive or fibrous forms.
Is this 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 actinolite with a known reference. Actinolite 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. Actinolite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Actinolite typically shows a vitreous to silky luster.
- 4Match the color rangeCompare against the expected color range: green, dark green, blackish-green, gray-green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic, acicular, fibrous, radiating masses.
Often confused with
Actinolite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads vitreous to silky on Actinolite and vitreous on Tremolite.
How to tell apart: Streak differs — Actinolite leaves white, Hornblende leaves grayish-white; luster reads vitreous to silky on Actinolite and vitreous on Hornblende.
How to tell apart: Tourmaline is the harder of the two (Mohs 7-7.5 vs. 5.5-6); luster reads vitreous to silky on Actinolite and vitreous on Tourmaline.
Often found alongside actinolite
Minerals reported to co-occur with actinolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂
- Mohs hardness
- 5.5-6
- Density
- 3.0-3.5 g/cm³
- Streak
- White
- Luster
- Vitreous to Silky
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic, Acicular, Fibrous, Radiating Masses
- Cleavage
- Perfect in Two Directions At 56 and 124 Degrees
- Rarity
- Common
- Uses
- Collector, Lapidary
- Host rock
- Metamorphic Rocks Like Greenschist and Contact Metamorphosed Limestone
- Typical price
- $5-50 thumbnail, $30-200 specimen
Where rockhounds find actinolite
31 mapped spotsClassic worldwide localities
- Ontario, Canada
- Zillertal, Austria
- Ticino, Switzerland
- New York, USA
- Val Malenco, Italy
U.S. states with actinolite
Each link opens a state-specific list of mapped rockhounding spots that produce actinolite.
Field-hunting tip
Look in metamorphic rocks like greenschist and contact metamorphosed limestone country — that is the host setting where actinolite typically forms. If you start seeing talc, calcite, dolomite in float, you are in the right ground. Field specimens usually show a prismatic, acicular, fibrous, radiating masses habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in North Carolina, Utah, Vermont — start trip planning there.
Common questions
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Find actinolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
