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Formula: Ca2B(AsO4)(OH)4
Compound arsenate
Crystal System: Tetragonal
Specific gravity: 3.156
Hardness: 3
Streak: White
Colour: Colorless to white, also golden brown; colourless in transmitted light.
Solubility: Readily soluble in dilute hydrochloric acid
Environments:
Pegmatites
Metamorphic environments
Cahnite is a rare arsenate.
Localities
At the Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in
veins of hydrothermal origin in skarn. Cahnite was first found here
in association with borcarite as pseudotetrahedral crystals in groups adhering
to the surfaces of much larger borcarite crystal clusters. The cahnite
crystals are greyish white and up to about 2 mm. Later finds were of pseudotetrahedral crystals of cahnite
associated with olshanskyite,
johnbaumite or roweite but not with
borcarite. The crystals of cahnite are white and opaque, to 3 mm, and
have faces that are rough and uneven
(R&M 96.5.400).
Cahnite from Shijiang Shan - Image
At Capo di Bove, Italy, cahnite occurs with zeolites in leucitic lava associated with
phillipsite, chabazite and
calcite
(HOM).
At Charcas, Charcas Municipality, San Luis Potosí, Mexico,
the primary minerals are
sphalerite, galena,
chalcopyrite, bornite,
tetrahedrite,
arsenopyrite, pyrite and
silver minerals such as jalpaite,
diaphorite and acanthite. In
the host rock, as metamorphic or alteration minerals, danburite,
datolite, hedenbergite,
epidote, chlorite,
andradite, actinolite
and wollastonite have been reported.
Quartz, calcite and
danburite crystallised during the entire life of the systems, throughout
the intrusive emplacement, metamorphism, and mineralising events. With depth, both
sphalerite and galena decrease
while chalcopyrite increases.
Secondary sulphides formed include
bornite, covellite,
digenite and chalcocite.
Native silver, native gold,
hematite and goethite were
deposited after the sulphides
(Minrec 55.6.727-728).
Cahnite crystals range from less than a 1 mm to 2 mm on rare occasions. It occurs as beige sphenoids
associated with borcarite and
calcite. Based on current (2024) knowledge, less than 10% of the
borcarite specimens have cahnite associated with them
(Minrec 55.6.737).
At the Kombat mine, Namibia, cahnite is associated with
natronambulite,
gypsum,
baryte and
calcite
(HOM).
Cahnite from the Kombat Mine - Image
In Siberia, Russia, cahnite is associated with svabite,
magnetite, sphalerite,
garnet and calcite
(HOM).
At the type locality, the Franklin Mine, New Jersey, USA, cahnite is a late-stage mineral in pegmatites cutting a metamorphosed
stratiform zinc orebody, associated with hedyphane,
friedelite,
pyrochroite, franklinite,
willemite, rhodonite,
datolite, axinite,
jarosewichite, samfowlerite,
flinkite, hodgkinsonite,
hetaerolite, hausmannite,
groutite, kentrolite,
garnet and baryte
(HOM , Mindat).
Cahnite from the Franklin Mine -
Image
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