An actinolite prism is a long, slender, often deeply striated monoclinic crystal ranging from pale to dark green. It occurs in metamorphic environments such as greenschist facies or contact metamorphic zones, commonly embedded in a talc or marble matrix.
Is this actinolite prism?
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 prism with a known reference. Actinolite Prism 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: bright green, dark green, blackish green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, acicular, fibrous.
Often confused with
Actinolite Prism vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside actinolite prism
Minerals reported to co-occur with actinolite prism. 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
- 3.0-3.2 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals, acicular, fibrous
- Cleavage
- Perfect in two directions
- Rarity
- Common
- Uses
- Collector, Lapidary
- Host rock
- metamorphic rocks
Where rockhounds find actinolite prism
1 mapped spotsClassic worldwide localities
- Ontario, Canada
- Zillertal, Austria
- Madagascar
- Switzerland
- New York, USA
Field-hunting tip
Where it forms: metamorphic rocks. If you start seeing quartz, talc, calcite in float, you are in the right ground. Typical habit: prismatic crystals, acicular, fibrous. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California. Start trip planning there.
More actinolite prism photos
Common questions
How do you identify actinolite prism?+
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Can I find actinolite prism in the United States?+
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Find actinolite prism on the map
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