Allanite-(Y) is a rare-earth-bearing member of the epidote group typically found in granitic pegmatites. It often displays a distinct black or brownish-black color and submetallic luster, and it is almost always metamict, meaning its crystal structure has been partially destroyed by radioactive decay.
Is this allanite-(y)?
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 allanite-(y) with a known reference. Allanite-(Y) sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: grayish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to greasy.
- 4Match the color rangeCompare against the expected color range: black, brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: disseminated, massive.
Often confused with
Allanite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Allanite-(Y) leaves grayish brown, Allanite-(Ce) leaves gray.
How to tell apart: Streak differs, so Allanite-(Y) leaves grayish brown, Allanite leaves gray; luster reads vitreous to greasy on Allanite-(Y) and submetallic on Allanite.
Often found alongside allanite-(y)
Minerals reported to co-occur with allanite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaYAl₂Fe(Si₂O₇)(SiO₄)O(OH)
- Mohs hardness
- 5.5
- Density
- 3.5-4.2 g/cm³
- Streak
- Grayish brown
- Luster
- Vitreous to greasy
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Disseminated, massive
- Cleavage
- Imperfect on {001}; imperfect on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- granite pegmatites, syenites
Where rockhounds find allanite-(y)
Classic worldwide localities
- Sweden
- Norway
- USA
- Russia
- Madagascar
Field-hunting tip
Where it forms: granite pegmatites, syenites. If you start seeing quartz, microcline, biotite in float, you are in the right ground. Typical habit: disseminated, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify allanite-(y)?+
Where is allanite-(y) found?+
Is allanite-(y) safe to handle?+
What rocks look like allanite-(y)?+
What minerals are found with allanite-(y)?+
What kind of rock does allanite-(y) form in?+
What is allanite-(y) used for?+
Find allanite-(y) on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
