Jimthompsonite is a rare chain silicate mineral often associated with anthophyllite in altered ultramafic rocks. It is best identified by its distinct bladed to fibrous habit and characteristic pinkish-brown color, often requiring X-ray diffraction to distinguish it definitively from associated pyroxene-group minerals.
Is this jimthompsonite?
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 jimthompsonite with a known reference. Jimthompsonite sits at Mohs 2-2.5, 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: silky to pearly.
- 4Match the color rangeCompare against the expected color range: colorless, pink brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: bladed crystals, fibrous aggregates.
Often confused with
Jimthompsonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside jimthompsonite
Minerals reported to co-occur with jimthompsonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₅Si₆O₁₆(OH)₂
- Mohs hardness
- 2-2.5
- Density
- 3.03 g/cm³
- Colors
- Streak
- White
- Luster
- Silky to pearly
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Bladed crystals, fibrous aggregates
- Cleavage
- Perfect on {210}, intersecting at 38° and 142°; breakage on {100} and {010} may be partings
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In the black wallrock between chlorite and actinolite zones of a metamorphosed ultramafic body
Where rockhounds find jimthompsonite
Classic worldwide localities
- Carleton talc quarry, near Chester, Windsor Co., Vermont, USA
Field-hunting tip
Where it forms: In the black wallrock between chlorite and actinolite zones of a metamorphosed ultramafic body. If you start seeing chesterite, clinojimthompsonite, anthophyllite in float, you are in the right ground. Typical habit: bladed crystals, fibrous aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify jimthompsonite?+
Where is jimthompsonite found?+
What rocks look like jimthompsonite?+
What minerals are found with jimthompsonite?+
What kind of rock does jimthompsonite form in?+
What is jimthompsonite used for?+
Find jimthompsonite on the map
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