Black derbylite microcrystals, a rare Fe-Ti-Sb oxide mineral only known from two localities worldwide, on a contrasting matrix. The specimens from Buca della Vena (Apuan Alps, Lucca Province, Tuscany, Italy) are, by far, the most aesthetic for the species — Photo: David Hospital · CC BY-SA 4.0
Derbylite
Derbylite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Fe³⁺₄Ti⁴⁺₃Sb³⁺O₁₃(OH).
It crystallizes in the monoclinic crystal system (space group P2_1/m).
Key properties: Mohs hardness 5; specific gravity 4.53–4.62; Resinous to metallic luster; optically biaxial.
IMA symbol Dby, grandfathered status — known before the IMA’s founding, named in 1897.
Found in cinnabar-bearing placer gravels (Tripuhy, Brazil); in microcrystalline barite and in cavities within metasomatically mineralized dolostones (Buca della Vena mine, Italy).
It is found associated with Roméite, tripuhyite, monazite, xenotime, zircon, rutile, hematite, muscovite (Tripuhy, Brazil); pyrite, sphalerite, bournonite, schafarzikite, versiliaite.
The name refers to the American geologist Orville Adelbert Derby (1851–1915), at one time Director of the Brazilian Geological Survey.