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.
Is this thomsenolite?
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 thomsenolite with a known reference. Thomsenolite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, pearly on cleavages.
- 4Match the color rangeCompare against the expected color range: colorless, white, reddish, brownish.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic, pseudo cubic.
Often confused with
Thomsenolite vs. its common look-alikes, and how to tell them apart in the field.
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
- 2.981 g/cm³
- Streak
- White
- Luster
- Vitreous, pearly on cleavages
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic, pseudo cubic
- Cleavage
- {001}, perfect; {110}, distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As an alteration product of cryolite and other alkali aluminum fluorides, most commonly in granite pegmatites
Where rockhounds find thomsenolite
Classic worldwide localities
- St. Peters Dome, near Pikes Peak, El Paso Co., Colorado, USA
- Spider mine, Honeycomb Hills, Juab Co., Utah, USA
- Quitman Mountains, Hudspeth Co., Texas, USA
- Morefield pegmatite mine, Amelia, Amelia Co., Virginia, USA
- Ivigtut cryolite deposit, southwestern Greenland
- Miass, Ilmen Mountains, Southern Ural Mountains, Southern Ural Mountains and other undefined localities in Russia
Field-hunting tip
Where it forms: As an alteration product of cryolite and other alkali aluminum fluorides, most commonly in granite pegmatites. If you start seeing cryolite, pachnolite, ralstonite in float, you are in the right ground. Typical habit: prismatic, pseudo cubic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify thomsenolite?+
Where is thomsenolite found?+
What rocks look like thomsenolite?+
What minerals are found with thomsenolite?+
What kind of rock does thomsenolite form in?+
What is thomsenolite used for?+
Find thomsenolite on the map
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