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 5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, silky.
- 4Match the color rangeCompare against the expected color range: green, dark green, blackish-green, gray-green, green black, black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: bladed, fibrous, radial.
Often confused with
Actinolite vs. its common look-alikes, and how to tell them apart in the field.
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
- 5-6
- Density
- 3.03-3.24 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous, silky
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Bladed, fibrous, radial
- Cleavage
- Good on {110}, with intersections of 56° and 124°; parting on {100}
- Rarity
- Common
- Uses
- Collector, Lapidary
- Host rock
- Produced by low-grade regional or contact metamorphism of magnesium carbonate, mafic, or ultramafic rocks; also in glaucophane-bearing blueschists
Where rockhounds find actinolite
31 mapped spotsClassic worldwide localities
- Gouverneur, St. Lawrence Co., New York, USA
- Franklin and Newton, Sussex Co., New Jersey, USA
- Chester, Windsor Co., Vermont, USA
- Fairfax quarry, Centreville, Fairfax Co., Virginia, USA
- Mt. Greiner, Zillertal, and at Untersulzbachtal, Austria
- Zermatt, Valais, Switzerland
U.S. states with actinolite
Each link opens a state-specific list of mapped rockhounding spots that produce actinolite.
Field-hunting tip
Where it forms: Produced by low-grade regional or contact metamorphism of magnesium carbonate, mafic, or ultramafic rocks; also in glaucophane-bearing blueschists. If you start seeing talc, epidote, chlorite in float, you are in the right ground. Typical habit: bladed, fibrous, radial. 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.
More actinolite photos
Common questions
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Find actinolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
