Black microcrystals of the very rare mineral freudenbergite from one of the only five known localities worldwide. Associated mineral is orange-brown rutile. From: Kaskasnyunchorr, Khibiny Massif, Kola, Russian Federation. — Photo: David Hospital · CC BY-SA 4.0
Freudenbergite
A sodium-titanate mineral named for Wilhelm Freudenberg, paleontologist and mineralogy curator at Karlsruhe.
Intro adapted from Wikipedia (CC BY-SA).
Freudenbergite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Na(Ti⁴⁺₃Fe³⁺)O₈.
It crystallizes in the monoclinic crystal system (space group C2/m).
Key properties: Mohs hardness 5; specific gravity 3.956; Pale yellow-brown streak; optically biaxial.
IMA symbol Fdb, IMA status: approved, named in 1961.
A late-stage mineral in an apatite-bearing alkali syenite.
It is found associated with Hematite, högbomite, diopside, apatite, ilmenite, titanite, biotite, sanidine.
The name refers to Professor Wilhelm Freudenberg (1881–?), who studied Katzenbuckel rocks.