Margarosanite is a rare lead-calcium silicate best known to collectors for its intense and distinctive bright white-to-blue fluorescence under shortwave ultraviolet light. It typically occurs as white, pearly platy crystals or massive granular aggregates in metamorphic environments, most notably the famous zinc mines of Franklin, New Jersey, and the mines at Långban, Sweden.
Is this margarosanite?
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 margarosanite with a known reference. Margarosanite sits at Mohs 2.5-3, 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: pearly on cleavage.
- 4Match the color rangeCompare against the expected color range: colorless, pearl white.
- 5Look at form & habitCrystal system: triclinic. Typical habit: cleaveable, granular, prismatic.
Often confused with
Margarosanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Wollastonite is the harder of the two (Mohs 4.5-5 vs. 2.5-3); luster reads pearly on cleavage on Margarosanite and vitreous, pearly on cleavage on Wollastonite.
How to tell apart: Pectolite is the harder of the two (Mohs 4.5-5 vs. 2.5-3); luster reads pearly on cleavage on Margarosanite and silky, subvitreous on Pectolite.
Often found alongside margarosanite
Minerals reported to co-occur with margarosanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂PbSi₃O₉
- Mohs hardness
- 2.5-3
- Density
- 3.99-4.33 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly on cleavage
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Cleaveable, granular, prismatic
- Cleavage
- Perfect on {010}, good on {100}, fair on {001}
- Fluorescence
- Red sky blue under SW UV; red orange under LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA)
Where rockhounds find margarosanite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
- Långban and Jakobsberg, Värmland, Sweden
Field-hunting tip
Where it forms: In a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA). If you start seeing nasonite, minehillite, almandine in float, you are in the right ground. Typical habit: cleaveable, granular, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify margarosanite?+
Where is margarosanite found?+
Is margarosanite safe to handle?+
What rocks look like margarosanite?+
What minerals are found with margarosanite?+
What kind of rock does margarosanite form in?+
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Find margarosanite on the map
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