Martinandresite is a rare barium aluminum silicate that forms white or tan platy crystals. It occurs in quartz veins cutting zoisite-, celsian-, and armenite-bearing gneiss. Associated minerals include armenite, quartz and dickite. It was first described from Wasenalp, near Isenwegg peak, Ganter valley, Simplon region, Switzerland.
Is this martinandresite?
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 martinandresite with a known reference. Martinandresite sits at Mohs 4.5, 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: vitreous to porcelaneous.
- 4Match the color rangeCompare against the expected color range: white, tan.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals.
Often confused with
Martinandresite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside martinandresite
Minerals reported to co-occur with martinandresite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ba₂(Al₄Si₁₂O₃₂)·10H₂O
- Mohs hardness
- 4.5
- Density
- 2.482 g/cm³
- Streak
- White
- Luster
- Vitreous to porcelaneous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy crystals
- Cleavage
- Indistinct, presumably on {010} and in a direction across (010)
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In quartz veins cutting zoisite-, celsian-, and armenite-bearing gneiss
Where rockhounds find martinandresite
Classic worldwide localities
- Wasenalp, near Isenwegg peak, Ganter valley, Simplon region, Switzerland
Field-hunting tip
Where it forms: In quartz veins cutting zoisite-, celsian-, and armenite-bearing gneiss. If you start seeing armenite, quartz, dickite in float, you are in the right ground. Typical habit: platy crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify martinandresite?+
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What rocks look like martinandresite?+
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Find martinandresite on the map
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