Thomsenolite is a mineral with formula: NaCaAlF₆·H₂O. It is an alteration product of

cryolite Cryolite ( Na3 Al F6, sodium hexafluoroaluminate) is a rare mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987. It is used in the reduction ("smelting") of aluminium, in pest ...

. It was discovered in 1868 in

Ivigtut Ivittuut (formerly, Ivigtût) ( Kalaallisut: "Grassy Place") is an abandoned mining town near Cape Desolation in southwestern Greenland, in the modern Sermersooq municipality on the ruins of the former Norse Middle Settlement. Ivittuut is one ...

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

and named for Hans Peter Jorgen Julius Thomsen (1826–1909).Mindat.org entry
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References

Sodium minerals Calcium minerals Aluminium minerals Fluorine minerals Monoclinic minerals Minerals in space group 14 Minerals described in 1868 {{halide-mineral-stub