Kupletskite-(Cs) is a rare member of the astrophyllite group characterized by a high cesium content. It typically forms thin, bronze-colored platy crystals in alkaline igneous environments, often closely resembling its common relative astrophyllite.
Is this kupletskite-(cs)?
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 kupletskite-(cs) with a known reference. Kupletskite-(Cs) sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellowish-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: brown, black.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy, rosette.
Often confused with
Kupletskite-(Cs) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Kupletskite-(Cs) is noticeably harder (Mohs ~4 vs. 3); streak differs, so Kupletskite-(Cs) leaves yellowish-brown, Astrophyllite leaves golden; luster reads dull on Kupletskite-(Cs) and submetallic, pearly, greasy on Astrophyllite.
How to tell apart: Streak differs, so Kupletskite-(Cs) leaves yellowish-brown, Kupletskite leaves brown; luster reads dull on Kupletskite-(Cs) and vitreous on Kupletskite.
Often found alongside kupletskite-(cs)
Minerals reported to co-occur with kupletskite-(cs). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cs₂NaMn₇Ti₂(Si₄O₁₂)₂O₂(OH)₄F
- Mohs hardness
- ~4
- Density
- 3.68 g/cm³
- Streak
- Yellowish-brown
- Luster
- Dull
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Platy, rosette
- Cleavage
- {001}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- At the border of aegirine-microcline-quartz pegmatites, and in polylithionite-quartz replacement complexes in pegmatites
Where rockhounds find kupletskite-(cs)
Classic worldwide localities
- Dara-i-Pioz massif, Alai Range, Tien Shan, Tajikistan
Field-hunting tip
Where it forms: At the border of aegirine-microcline-quartz pegmatites, and in polylithionite-quartz replacement complexes in pegmatites. If you start seeing pyrochlore, stillwellite, tienshanite in float, you are in the right ground. Typical habit: platy, rosette. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kupletskite-(cs)?+
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What rocks look like kupletskite-(cs)?+
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Find kupletskite-(cs) on the map
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