Stillwellite-(Ce) is a rare borosilicate mineral typically found in complex rare-earth element deposits. It usually occurs as trigonal prismatic crystals or massive, irregular grains within metasomatized rocks, often associated with other rare earth minerals.
Is this stillwellite-(ce)?
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 stillwellite-(ce) with a known reference. Stillwellite-(Ce) 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. Stillwellite-(Ce) leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Stillwellite-(Ce) typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, pink, yellowish-white, brownish-yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: trigonal prisms or massive grains.
Often confused with
Stillwellite-(Ce) vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Stillwellite-(Ce) leaves white, Allanite leaves gray; luster reads vitreous on Stillwellite-(Ce) and submetallic on Allanite.
How to tell apart: Luster reads vitreous on Stillwellite-(Ce) and resinous on Monazite.
Often found alongside stillwellite-(ce)
Minerals reported to co-occur with stillwellite-(ce). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ce,La,Ca)BSiO₅
- Mohs hardness
- 5
- Density
- 4.57 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Trigonal Prisms or Massive Grains
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific Study
- Host rock
- Metasomatized Alkaline Igneous Rocks and Rare Earth Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find stillwellite-(ce)
Classic worldwide localities
- Mount Isa, Queensland, Australia
- Kola Peninsula, Russia
- Central Asia rare earth deposits
Field-hunting tip
Look in metasomatized alkaline igneous rocks and rare earth deposits country — that is the host setting where stillwellite-(ce) typically forms. If you start seeing allanite, apatite, fluorite in float, you are in the right ground. Field specimens usually show a trigonal prisms or massive grains habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find stillwellite-(ce) on the map
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