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Formula: Fe3+4Ti4+3Sb3+O13(OH)
Antimonite, titanium-bearing
mineral
Crystal System: Monoclinic
Specific gravity: 4.53 to 4.62 measured, 4.76 calculated
Hardness: 5
Streak: Brown
Colour: Pitch-black, dark brown when translucent
Luminescence: Not fluorescent under UV
Solubility: Not soluble in acids
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the type locality, Tripuí, Amarantina district, Ouro Preto, Minas Gerais, Brazil, derbylite occurs as
small grains and complex prismatic crystals in cinnabar-bearing
placer gravels. Associated minerals include
roméite, tripuhyite,
monazite, xenotime,
zircon, rutile,
hematite and muscovite
(HOM).
The Buca della Vena Mine, Pontestazzemese, Stazzema, Lucca Province, Tuscany, Italy, is an
iron mine where the ore (magnetite
hematite and minor pyrite) occurs
within a microcrystalline mass of baryte. The mineralisation is attributed
to metasomatism by medium-temperature hydrothermal fluids introduced along the contact between
phyllite and
dolostone. Veins of recrystallized
dolomite and baryte occur within
the microcrystalline mineralised body as well as at the contact between this body and the surrounding
dolostone country rock. Derbylite occurs in these veins, in
cavities inside the veins or embedded within the recrystallised dolomite
or baryte. Associated minerals are
pyrite, sphalerite,
bournonite, schafarzikite,
versiliaite and apuanite.
Derbylite is very rare; less than ten specimens are known. It is present here as euhedral, black prismatic
crystals up to 2 mm long, with a metallic lustre and conchoidal fracture
(CM 21.3.513-516).
At the Monte Arsiccio Mine, Sant'Anna di Stazzema, Stazzema, Lucca Province, Tuscany, Italy, derbylite occurs
as prismatic to acicular black crystals in carbonate veins. Graeserite
is also found here
(MM 84.5.766-777).
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