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 5.5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferriallanite-(La) leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Ferriallanite-(La) typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-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 — Ferriallanite-(La) leaves brown, Allanite-(Ce) leaves greyish-white.
How to tell apart: Streak differs — Ferriallanite-(La) leaves brown, Epidote leaves white; luster reads submetallic on Ferriallanite-(La) and vitreous on Epidote.
How to tell apart: Luster reads submetallic on Ferriallanite-(La) and vitreous 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
- 5.5-6
- Density
- 4.2-4.5 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Igneous Rocks, Granitic Pegmatites
- Typical price
- $50-300 per specimen
Where rockhounds find ferriallanite-(la)
Classic worldwide localities
- Kola Peninsula, Russia
- Hokkaido, Japan
- Sweden
Field-hunting tip
Look in alkaline igneous rocks, granitic pegmatites country — that is the host setting where ferriallanite-(la) typically forms. If you start seeing quartz, feldspar, titanite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferriallanite-(la) on the map
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