Cayalsite-(Y) is a rare yttrium-dominant silicate mineral belonging to the gadolinite group. It typically occurs as dark, vitreous, prismatic crystals within rare-earth-enriched pegmatites and requires precise chemical analysis for definitive identification.

Hardness

6.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Opaque

mineralrareGadolinite Group family

Cayalsite-(Y)

Hardness: 6.5
Luster: Vitreous
Streak: White
Transparency: Opaque

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Is this cayalsite-(y)?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch cayalsite-(y) with a known reference. Cayalsite-(Y) sits at Mohs 6.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Cayalsite-(Y) leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Cayalsite-(Y) typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: black, brownish-black, brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: prismatic crystals.

Often confused with

Cayalsite-(Y) vs. its common look-alikes — and how to tell them apart in the field.

How to tell apart: Streak differs — Cayalsite-(Y) leaves white, Allanite leaves gray; luster reads vitreous on Cayalsite-(Y) and submetallic on Allanite.

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Often found alongside cayalsite-(y)

Minerals reported to co-occur with cayalsite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Y₂Fe²⁺Be₂Si₂O₁₀
Mohs hardness: 6.5
Density: 4.6-4.9 g/cm³
Colors: Black Brownish-black Brown
Streak: White
Luster: Vitreous
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Prismatic Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Syenite Pegmatites
Typical price: $50-300 per specimen

Where rockhounds find cayalsite-(y)

Classic worldwide localities

Tvedalen, Larvik, Norway
Baveno, Italy
Mount Malosa, Malawi

Field-hunting tip

Look in syenite pegmatites country — that is the host setting where cayalsite-(y) typically forms. If you start seeing quartz, microcline, zircon in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cayalsite-(y)?+

Mohs hardness is 6.5. It typically shows a vitreous luster. The streak is white. Common colors include black, brownish-black, brown.

Where is cayalsite-(y) found?+

Notable localities include Tvedalen, Larvik, Norway; Baveno, Italy; Mount Malosa, Malawi.

How much is cayalsite-(y) worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is cayalsite-(y) safe to handle?+

This mineral is radioactive. Contains minor amounts of radioactive thorium/uranium impurities; avoid dust inhalation and wash hands after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like cayalsite-(y)?+

Cayalsite-(Y) is most often confused with Gadolinite-(Y), Allanite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with cayalsite-(y)?+

Cayalsite-(Y) commonly co-occurs with Quartz, Microcline, Zircon, Fluorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cayalsite-(y) form in?+

Cayalsite-(Y) typically forms in syenite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is cayalsite-(y) used for?+

Cayalsite-(Y) is used in collector.

Find cayalsite-(y) on the map

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