Kostylevite is a rare zirconium silicate mineral discovered in the alkaline massifs of the Kola Peninsula. It typically occurs as small, colorless prismatic crystals found within pegmatite veins associated with eudialyte-group minerals.
Is this kostylevite?
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 kostylevite with a known reference. Kostylevite sits at Mohs ~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, light yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, radial aggregates.
Often confused with
Kostylevite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Vlasovite is the harder of the two (Mohs 6 vs. ~5); luster reads vitreous on Kostylevite and greasy; highly vitreous to pearly on cleavage surfaces on Vlasovite.
How to tell apart: Luster reads vitreous on Kostylevite and weakly vitreous or dull on Catapleiite.
Often found alongside kostylevite
Minerals reported to co-occur with kostylevite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₄Zr₂Si₆O₁₈·2H₂O
- Mohs hardness
- ~5
- Density
- 2.74 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals, radial aggregates
- Cleavage
- {110}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In alkalic pegmatite in a differentiated alkalic massif
Where rockhounds find kostylevite
Classic worldwide localities
- Yuonnemiok River Valley, eastern Khibiny Massif, Kola Peninsula, Russa (type locality)
Field-hunting tip
Where it forms: In alkalic pegmatite in a differentiated alkalic massif. If you start seeing umbite, wadeite, eudialyte in float, you are in the right ground. Typical habit: prismatic crystals, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kostylevite?+
Where is kostylevite found?+
What rocks look like kostylevite?+
What minerals are found with kostylevite?+
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Find kostylevite on the map
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