Kupletskite is a rare silicate mineral belonging to the astrophyllite group, often appearing as distinct dark, platy, or radiating blades. It is primarily found in alkaline pegmatites and is highly prized by collectors for its aesthetic crystal formations and its close chemical relationship to the more common astrophyllite.
Is this kupletskite?
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 with a known reference. Kupletskite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Kupletskite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Kupletskite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: dark brown, reddish-brown, black.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy crystals, radiating blades, lamellar aggregates.
Often confused with
Kupletskite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Kupletskite leaves brown, Astrophyllite leaves golden-brown.
How to tell apart: Streak differs — Kupletskite leaves brown, Niobophyllite leaves yellowish-brown; luster reads submetallic on Kupletskite and pearly on Niobophyllite.
Often found alongside kupletskite
Minerals reported to co-occur with kupletskite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂Na(Mn,Fe)₇Ti₂Si₈O₂₆(OH)₄F
- Mohs hardness
- 3-4
- Density
- 3.32 g/cm³
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Platy Crystals, Radiating Blades, Lamellar Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Igneous Rocks, Pegmatites
- Typical price
- $20-150 for small specimens
Where rockhounds find kupletskite
Classic worldwide localities
- Lovozero Massif, Russia
- Khibiny Massif, Russia
- Mont Saint-Hilaire, Canada
Field-hunting tip
Look in alkaline igneous rocks, pegmatites country — that is the host setting where kupletskite typically forms. If you start seeing aegirine, nepheline, microcline in float, you are in the right ground. Field specimens usually show a platy crystals, radiating blades, lamellar aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find kupletskite on the map
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