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Formula: NaAl(AsO4)F
Arsenate, tilasite group,
forms series with tilasite and with
maxwellite
Crystal System: Monoclinic
Specific gravity: 3.94 to 4.07 measured, 3.616 calculated
Hardness: 5½
Streak: Cream-yellow
Colour: Light to dark orange-red, red, green; orange-yellow in artificial light
Luminescence: Not fluorescent under either short wave or long wave UV
Solubility: Insoluble in aqua regia, slowly soluble in either HCI or HNO, readily soluble in hot, concentrated
sulphuric acid
Magnetism: Not magnetic
Common impurities:
Environments
Volcanic igneous environments
Pegmatites
Durangite occurs in veins in alkalic rhyolite and in
placers derived therefrom, also in
pegmatite dikes in
granite. Associated minerals include
cassiterite, hematite,
topaz, ilmenite,
tantalite, wickmanite,
beudantite, mimetite,
fluorite, tridymite,
cristobalite, quartz,
amblygonite, chalcedony,
zeolites and clay minerals
(HOM).
Localities
At the type locality, the Barranca Mine, Coneto de Comonfort, Coneto de Comonfort Municipality, Durango, Mexico,
durangite occurs in tin-bearing veins associated with
cassiterite, hematite
(including the variety specularite),
quartz, tridymite,
cristobalite, opal,
chalcedony, fluorite,
topaz, mimetite,
sanidine, montmorillonite
and zeolites. It has also been reported in residual and alluvial
placer deposits derived from the
tin veins.
The only major difference between the Black Range (see below) and Coneto assemblages is the presence of
beudantite in the Black Range as an alteration product and coexisting
mineral with durangite, rather than mimetite, which is found
associated with the durangite at Coneto
(CM 23.2.241-246).
Durangite from the Barranca Mine - Image
The Black Range, New Mexico, USA, hosts the 74 Draw deposits and Boiler Peak, both in Sierra County. In these Black
Range locations, durangite occurs as small grains and aggregates in veins and veinlets several centimetres
in width within zones of alteration in an alkali rhyolite host-rock.
The veins form reticulate networks 3 to 100 metres wide. The minerals in these veins include, in generalised
paragenetic sequence, with some minerals occurring in multiple generations,
hematite (much of it specularite),
wood tin,
,
cassiterite, wood tin,
durangite, hematite,
silica paramorphs
quartz, tridymite and
cristobalite, durangite,
beudantite, fluorite,
cristobalite, pink to white dioctahedral
smectite, todorokite, and
disordered, red-brown dioctahedral smectite. A red-brown to orange-red
Ca-Fe clinopyroxene was found associated with the durangite at
Seventyfour Draw but was not found at Boiler Peak.
Durangite from the Black Range is pale yellow-orange to medium orange-red and is clear to semi-translucent
where fresh. Individual crystals reach 2 mm in maximum dimension, but most are less than 0.5 mm across.
Durangite from all localities has a vitreous lustre, a pale yellow streak and shows irregular and conchoidal
fracture and one good cleavage
(CM 23.2.241-246).
At 74 Draw deposits, Sierra County, New Mexico, USA, the durangite is generally pale to medium yellow-orange
or orange rather than orange-red. Individual grains are 0.5 mm across or more. The associated minerals are the same
as described for Boiler Peak (see below) except that the white, fine-grained mixture of
fluorite, montmorillonite
and cristobalite is less abundant here.
Fluorite also occurs locally as clear, grey, discrete botryoidal masses.
Much of the final generation of cassiterite is in the form of rounded
clumps of slender, almost white, acicular needles. Some of these clumps are several millimetres across; individual
needles of cassiterite are as much as 200 pm long but only 10 pm or so
wide. Euhedral, prismatic crystals and some euhedral, squat, tabular crystals of red-brown to orange-red or orange
clinopyroxene, some of which exceed 2 mm in width, are intermixed with the
cassiterite - fluorite -
hematite - durangite association
(CM 23.2.241-246).
At Boiler Peak, Sierra County, New Mexico, USA, durangite occurs as pale yellow to medium reddish orange
grains and aggregates. The grains are as much as 0.5 mm across, and the aggregates up to 2 mm across. The bulk of
the durangite occurs as etched and altered material within the mineralised veinlets. Some grains
are very clear, unfractured and unaltered. Deposition of the durangite was contemporaneous with
deposition of crystalline cassiterite and
wood tin, hematite, and the
silica polymorphs. The durangite encloses and is enclosed by
these minerals. Extremely fine-grained white fluorite, admixed with
cristobalite and dioctahedral
montmorillonite, was subsequently deposited. Yellow-green,
fine-grained beudantite was deposited still later; some of the
beudantite apparently crystallised along with the durangite, and some
is pseudomorphic after it. The final products of deposition within the
open spaces of the veins are black, sooty, fine-grained lead-rich
todorokite and sticky, deep red-brown, disordered dioctahedral
smectite containing fragments of the previously mentioned minerals
(CM 23.2.241-246).
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