Pale tan crystal aggregates of dalyite associated to very minoritary orange brown janhaugite. Both are very rare zirconium minerals. From: Gjerdingen, Nordmarka, Lunner, Oppland, Norway. — Photo: David Hospital · CC BY-SA 4.0
Janhaugite
Janhaugite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₃Mn²⁺₃Ti₂(Si₂O₇)₂(O,OH,F)₄.
It crystallizes in the monoclinic crystal system (space group P2_1/n). It is a member of the Wöhlerite structural group.
Key properties: Mohs hardness 5; specific gravity 3.6; Light brown streak; Vitreous luster; optically biaxial.
IMA symbol Jhg, IMA status: approved, named in 1981.
Found in both the groundmass and miarolitic cavities in sodium-rich granite.
It is found associated with Pyrophanite, elpidite, monazite, dalyite, kupletskite.
The mineral was named to honor Jan Haug, an amateur mineralogist who first observed the mineral.