Rustumite is a rare calcium silicate chloride mineral typically found in high-temperature metamorphic environments such as spurrite skarns. It often appears as colorless to white tabular crystals or massive aggregates within complex mineral assemblages. It was first identified in the Chegem caldera and is highly sought after by systematic mineral collectors.
Is this rustumite?
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 rustumite with a known reference. Rustumite 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.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, massive, granular.
Often confused with
Rustumite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside rustumite
Minerals reported to co-occur with rustumite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₁₀(Si₂O₇)₂(SiO₄)(OH)₂Cl₂
- Mohs hardness
- 4-5
- Density
- 2.835 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, massive, granular
- Cleavage
- Poor on {100}, very poor on {010} and {001}
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In limestones between two ring dikes, formed during a metamorphic period in which H2O:CO2 in the vapor phase was relatively high (Kilchoan, Scotland)
Where rockhounds find rustumite
Classic worldwide localities
- Kilchoan, Ardnamurchan, Argyllshire, Scotland
- Carlingford, Co. Louth, Ireland
- Igeltjärn mine, near Persberg, Värmland, Sweden
- Güneyce-_ Ikizdere area, Trabzon Province, Turkey
- La Negra mine, Maconi, Querétaro, Mexico
Field-hunting tip
Where it forms: In limestones between two ring dikes, formed during a metamorphic period in which H2O:CO2 in the vapor phase was relatively high (Kilchoan, Scotland). If you start seeing åkermanite, merwinite, larnite in float, you are in the right ground. Typical habit: tabular crystals, massive, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rustumite?+
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What rocks look like rustumite?+
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Find rustumite on the map
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