Thomasclarkite-(Y) is an extremely rare carbonate mineral found primarily in the alkaline rocks of the Poudrette quarry at Mont Saint-Hilaire. It typically forms thin, white to colorless platy crystals and is highly prized by advanced micromount collectors due to its restricted type locality.

Hardness

Mohs

Luster

Pearly

Streak

White

Transparency

Transparent

mineralrare

Thomasclarkite-(Y)

Hardness: 3
Luster: Pearly
Streak: White
Transparency: Transparent

Is this thomasclarkite-(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 thomasclarkite-(y) with a known reference. Thomasclarkite-(Y) sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Thomasclarkite-(Y) leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Thomasclarkite-(Y) typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: white, colorless.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy crystals.

Often confused with

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

How to tell apart: Luster reads pearly on Thomasclarkite-(Y) and vitreous on Weloganite.

Compare →

Often found alongside thomasclarkite-(y)

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

All properties

Chemical formula: Na(Y,REE)(HCO₃)(OH)₃·4H₂O
Mohs hardness: 3
Density: 2.71 g/cm³
Colors: White Colorless
Streak: White
Luster: Pearly
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Platy Crystals
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Alkaline Igneous Intrusions
Typical price: $100-500 thumbnail

Where rockhounds find thomasclarkite-(y)

Classic worldwide localities

Mont Saint-Hilaire, Quebec, Canada

Field-hunting tip

Look in alkaline igneous intrusions country — that is the host setting where thomasclarkite-(y) typically forms. If you start seeing dawsonite, weloganite, quartz in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thomasclarkite-(y)?+

Mohs hardness is 3. It typically shows a pearly luster. The streak is white. Common colors include white, colorless.

Where is thomasclarkite-(y) found?+

Notable localities include Mont Saint-Hilaire, Quebec, Canada.

How much is thomasclarkite-(y) worth?+

Typical asking prices fall in the range of $100-500 thumbnail. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like thomasclarkite-(y)?+

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

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

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

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

Thomasclarkite-(Y) typically forms in alkaline igneous intrusions. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thomasclarkite-(y) used for?+

Thomasclarkite-(Y) is used in collector.

Find thomasclarkite-(y) on the map

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