Tremolite is a calcium magnesium silicate commonly found in metamorphosed carbonate rocks. It typically forms elongate, prismatic crystals or fibrous masses, and can sometimes transition into the iron-rich variety actinolite. Collectors should be aware that fibrous habits may present as asbestos, requiring careful handling.
Is this tremolite?
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 tremolite with a known reference. Tremolite 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.
- 4Match the color rangeCompare against the expected color range: white, gray, green, brown, colorless, light green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: columnar, massive.
Often confused with
Tremolite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside tremolite
Minerals reported to co-occur with tremolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- □Ca₂(Mg₅.₀₋₄.₅Fe₀.₀₋₀.₅)Si₈O₂₂(OH)₂
- Mohs hardness
- 5-6
- Density
- 2.99-3.03 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Columnar, massive
- Cleavage
- Perfect on {110}, intersecting at 56° and 124°; partings on {010}, {100}
- Fluorescence
- Yellow under SW UV; orange pink under LW UV
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- From contact metamorphism of Ca-Mg siliceous sediments; in greenschist facies metamorphics derived from ultramafic or magnesium carbonate rocks
Where rockhounds find tremolite
14 mapped spotsClassic worldwide localities
- Pierrepont, Gouverneur, Edwards, and Macomb, St. Lawrence Co., New York, USA
- Franklin, Sussex Co., New Jersey, USA
- Lee, Berkshire Co., Massachusetts, USA
- Campolungo Alp, Ticino, and Bristenstock, Uri, Switzerland
- St. Marcel, Piedmont, Italy
- Bilin, Czech Republic
Field-hunting tip
Where it forms: From contact metamorphism of Ca-Mg siliceous sediments; in greenschist facies metamorphics derived from ultramafic or magnesium carbonate rocks. If you start seeing calcite, dolomite, calcian garnet in float, you are in the right ground. Typical habit: columnar, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New York, Utah, New Jersey. Start trip planning there.
More tremolite photos
Common questions
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Find tremolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
