Ferriallanite-(La) is a rare rare-earth element silicate member of the allanite group, typically characterized by its black, submetallic appearance. It is primarily found in complex pegmatites and alkaline rock complexes, often requiring X-ray diffraction or chemical analysis for positive identification due to its similarity to other allanite group species.
Is this ferriallanite-(la)?
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 ferriallanite-(la) with a known reference. Ferriallanite-(La) sits at Mohs ~6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, massive.
Often confused with
Ferriallanite-(La) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferriallanite-(La) leaves brown, Allanite-(Ce) leaves gray.
How to tell apart: Streak differs, so Ferriallanite-(La) leaves brown, Epidote leaves grayish white.
How to tell apart: Luster reads vitreous on Ferriallanite-(La) and resinous on Ferriallanite-(Ce).
Often found alongside ferriallanite-(la)
Minerals reported to co-occur with ferriallanite-(la). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaLaFe³⁺AlFe²⁺Si₃O₁₂OH
- Mohs hardness
- ~6
- Density
- 4.099 g/cm³
- Colors
- Streak
- Brown
- Luster
- Vitreous
- Transparency
- Translucent in thin splinters
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a void in a sanidinite xenolith in pumice
Where rockhounds find ferriallanite-(la)
Classic worldwide localities
- Den Dellen pumice quarries, Niedermendig, Mendig, Laach Lake volcanic complex, Eifel Mountains, Rhineland-Palatinate, Germany (type locality)
- Mochalin Log deposit, Chelyabinsk Oblast, South Urals, Russia
Field-hunting tip
Where it forms: In a void in a sanidinite xenolith in pumice. If you start seeing sanidine, magnetite, nosean in float, you are in the right ground. Typical habit: prismatic crystals, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferriallanite-(la)?+
Where is ferriallanite-(la) found?+
Is ferriallanite-(la) safe to handle?+
What rocks look like ferriallanite-(la)?+
What minerals are found with ferriallanite-(la)?+
What kind of rock does ferriallanite-(la) form in?+
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Find ferriallanite-(la) on the map
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