Trimerite is a rare beryllium-manganese silicate primarily known from the Långban mines and the Franklin Mining District. It is highly prized by collectors for its distinct, bright yellow-green fluorescence under ultraviolet light. It typically occurs as small, tabular crystals or massive aggregates embedded within metamorphic manganese-bearing rocks.
Is this trimerite?
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 trimerite with a known reference. Trimerite sits at Mohs 6-7, 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, brilliant.
- 4Match the color rangeCompare against the expected color range: colorless, yellowish red, pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic, pseudo hexagonal, tabular.
Often confused with
Trimerite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside trimerite
Minerals reported to co-occur with trimerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaMn₂(BeSiO₄)₃
- Mohs hardness
- 6-7
- Density
- 3.474 g/cm³
- Streak
- White
- Luster
- Vitreous, brilliant
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic, pseudo hexagonal, tabular
- Cleavage
- Distinct on {001}
- Fluorescence
- Bright yellow-green under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare mineral, probably formed during late-stage hydrothermal activity associated with contact metamorphism and metasomatism
Where rockhounds find trimerite
Classic worldwide localities
- Harstigen mine, near Persberg, at Jakobsberg, and at Långban, Värmland, Sweden
Field-hunting tip
Where it forms: A rare mineral, probably formed during late-stage hydrothermal activity associated with contact metamorphism and metasomatism. If you start seeing calcite, hematite in float, you are in the right ground. Typical habit: prismatic, pseudo hexagonal, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify trimerite?+
Where is trimerite found?+
Is trimerite safe to handle?+
What rocks look like trimerite?+
What minerals are found with trimerite?+
What kind of rock does trimerite form in?+
What is trimerite used for?+
Find trimerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
