Merwinite is a rare nesosilicate mineral typically found in high-temperature contact metamorphic zones where limestones have been altered by igneous intrusions. It most commonly appears as colorless or pale green granular masses rather than well-defined crystals. It is a prized specimen for advanced collectors specializing in skarn mineralogy.
Is this merwinite?
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 merwinite with a known reference. Merwinite sits at Mohs 6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Merwinite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Merwinite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, pale green, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: granular, massive, or as rare small prismatic crystals.
Often confused with
Merwinite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside merwinite
Minerals reported to co-occur with merwinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₃Mg(SiO₄)₂
- Mohs hardness
- 6
- Density
- 3.15-3.20 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Granular, Massive, Or as Rare Small Prismatic Crystals
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Contact Metamorphosed Limestone (skarn Deposits)
- Typical price
- $20-100 per specimen
Where rockhounds find merwinite
Classic worldwide localities
- Crestmore, California, USA
- Carlingford, Ireland
- Kilchoan, Scotland
- Fuka, Japan
Field-hunting tip
Look in contact metamorphosed limestone (skarn deposits) country — that is the host setting where merwinite typically forms. If you start seeing larnite, gehlenite, calcite in float, you are in the right ground. Field specimens usually show a granular, massive, or as rare small prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify merwinite?+
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Find merwinite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
