Thomsenolite is a rare fluoride mineral often found as an alteration product of cryolite in pegmatitic environments. It is best identified by its prismatic to pseudo-octahedral habits and its distinct association with the Greenland cryolite deposit.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrare

Thomsenolite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this thomsenolite?

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 thomsenolite with a known reference. Thomsenolite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Thomsenolite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Thomsenolite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, pale yellow, brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: prismatic crystals, massive, granular.

Often confused with

Thomsenolite vs. its common look-alikes — and how to tell them apart in the field.

mineral

Pachnolite

Mohs 3

How to tell apart: Pachnolite is the harder of the two (Mohs 3 vs. 2).

How to tell apart: Luster reads vitreous on Thomsenolite and vitreous to greasy on Cryolite.

Compare →

Often found alongside thomsenolite

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

All properties

Chemical formula: NaCaAlF₆·H₂O
Mohs hardness: 2
Density: 2.95-3.0 g/cm³
Colors: Colorless White Pale Yellow Brown
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Prismatic Crystals, Massive, Granular
Cleavage: Good in One Direction
Rarity: Rare
Uses: Collector
Host rock: Cryolite-bearing Pegmatites
Typical price: $20-200 depending on specimen quality

Where rockhounds find thomsenolite

Classic worldwide localities

Ivittuut, Greenland
St. Peters Dome, USA
Miass, Russia

Field-hunting tip

Look in cryolite-bearing pegmatites country — that is the host setting where thomsenolite typically forms. If you start seeing cryolite, pachnolite, siderite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thomsenolite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, pale yellow, brown.

Where is thomsenolite found?+

Notable localities include Ivittuut, Greenland; St. Peters Dome, USA; Miass, Russia.

How much is thomsenolite worth?+

Typical asking prices fall in the range of $20-200 depending on specimen quality. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like thomsenolite?+

Thomsenolite is most often confused with Pachnolite, Cryolite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with thomsenolite?+

Thomsenolite commonly co-occurs with Cryolite, Pachnolite, Siderite, Fluorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thomsenolite form in?+

Thomsenolite typically forms in cryolite-bearing pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thomsenolite used for?+

Thomsenolite is used in collector.

Find thomsenolite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.