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Formula: Sb3+6+xO8+x(SO4)(OH)x(H2O)<1-x (x = 0.3)
Sulphate, antimony-bearing mineral
Crystal System: Triclinic
Specific gravity: 5.78 calculated
Hardness: 3 to 4
Streak: White
Colour: Colourless
Luminescence: No fluorescence observed under short wave or long wave UV
Environments
Sedimentary environments
Hydrothermal environments
Coquandite occurs in association with klebelsbergite,
peretaite, valentinite,
senarmontite, stibiconite,
stibnite, sulphur,
gypsum and quartz
(HOM).
Localities
There are two co-type localities, the Pereta Mine, Scansano, Grosseto Province, Tuscany, Italy, and the Lucky Knock
Mine, Okanogan County, Washington, USA.
At the Pereta Mine, Scansano, Grosseto Province, Tuscany, Italy, the main geological formations outcropping in the
area are, from bottom to top, the 'Calcare Cavernoso' limestone,
the 'Macigno' sandstone, and sands and
clays of the 'Neoautoctono Toscano'. A
stibnite vein with
quartzitic gangue fills a
fracture in the limestone, which appears to be thoroughly
silicised. Coquandite usually occurs as white powdery masses enbedded between the needles of columnar
stibnite, or as thin crusts with a pearly lustre. It appears sometimes
as spheroidal knobs of feathery aggregates of silky fibres, and, rarely, as tiny flexible lamellar crystals on
stibnite and quartz in cavities
in the limestone. Coquandite is strictly associated with
klebelsbergite and
peretaite, and is also associated with
valentinite,
senarmontite, sulphur,
gypsum and stibiconite. Like
klebelsbergite and
peretaite, coquandite was probably formed by the action of
sulphuric acid on stibnite.
Coquandite crystals occur as tiny transparent to translucent elongated colourless individuals, that are
flexible and often display an onion-skin aspect
(MM 56.599-603).
Coquandite from the Pereta Mine -
Image
At Le Cetine di Cotorniano Mine, Chiusdino, Siena Province, Tuscany, Italy, the environment in which
coquandite was found is similar to that of Pereta. The ore at the Cetine mine consists of
stibnite in small pods disseminated within the highly silicified
limestone of the 'Calcare Cavernoso' formation. Coquandite,
which is very rare in this locality, occurs as minute tabular crystals on
stibnite or quartz, in small
cavities in the limestone. The associated minerals are the same
as observed at Pereta, namely strictly associated with
klebelsbergite and
peretaite, and also associated with
valentinite,
senarmontite, sulphur,
gypsum and stibiconite
(MM 56.599-603).
Coquandite from Le Cetine di Cotorniano
Mine - Image
At the Lucky Knock Mine, Okanogan County, Washington, USA, coquandite appears as silky fibres or small
platelets implanted on stibnite or
stibiconite needles
(MM 56.599-603).
Coquandite from the Lucky Knock Mine -
Image
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