Outstanding reddish-brown dorrite crystals from Chelyabinsk, Chelyabinsk Oblast, Russian Federation. Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Dorrite
A silicate isostructural with the aenigmatite group — essentially rhönite without titanium, with ferric iron in its place.
Intro adapted from Wikipedia (CC BY-SA).
Dorrite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₄[Mg₃Fe³⁺₉]O₄[Si₃Al₈Fe³⁺O₃₆].
It crystallizes in the triclinic crystal system. It is a member of the Sapphirine structural group.
Key properties: Mohs hardness 5; specific gravity 3.959; Gray streak; Submetallic luster.
IMA symbol Dor, IMA status: approved, named in 1987.
A product of oxidizing, high-temperature, low-pressure metamorphism of alkalic rocks, in a pyrometamorphic zone in sediments.
It is found associated with Esseneite, titanian andradite, magnetite-magnesioferrite-spinel, plagioclase, gehlenite-åkermanite, wollastonite, ulvöspinel, nepheline, apatite.
The mineral was named to honor Dr. John A. Dorr, Jr., Professor of Geology, University of Michigan, Ann Arbor, Michigan, USA, in recognition of his regional geologic research in Wyoming.