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Formula: CaMg3(CO3)4
Anhydrous normal carbonate
Crystal System: Trigonal
Specific gravity: 2.696 measured, 2.87 calculated
Hardness: 1 to 2
Streak: White
Colour: White
Environments
Sedimentary environments
Cave deposits
Huntite occurs in caves where rocks are magnesium-rich, as a near-surface weathering product of rocks containing
brucite, dolomite,
magnesite and serpentine, and
as a diagenetic product
in recent sediments (Dana). It is typically precipitated by evaporative concentration of meteoric solutions
weathering
magnesite- or dolomite- bearing
rocks, or
serpentinite. Associated
minerals include magnesite,
dolomite,
aragonite, calcite and
hydromagnesite
(HOM).
Localities
At the Tea Tree Gully, South Mt Lofty Ranges, Mt Lofty Ranges, South Australia, huntite occurs at depths of up
to 30 feet below the
surface, as nodules associated with a dolomite horizon. Weathering of the
dolomite has resulted in calcite
being formed; the
magnesium in part has formed nodules of magnesite and in part percolated
down into fissures and
precipitated as huntite. No evidence was found of the huntite replacing
dolomite or
magnesite
(AM 52.1332-1340).
.
At the Grotte de la Clamouse, Saint-Jean-de-Fos, Lodève, Hérault, Occitanie, France, huntite has been found as
a precipitated
carbonate in caves in dolostone. It was precipitated from waters which had become relatively
rich in magnesium after traversing the dolostone
(AM 52.1332-1340).
In the Emirate of Abu Dhabi, United Arab Emirates, along the Trucial Coast, the partial infilling of marine lagoons by recent carbonate
sediments has formed a coastal plain which lies just above the level of normal high tides. The carbonate sediments are predominantly of
aragonite. Huntite has been found in the unlithifred sediments of the coastal plain. It
occurs in the upper 16 inches of the sediments, as irregular wisps and blebs to 0.3 inches, associated with a sandy mud of detrital
quartz and carbonates, together with abundant corroded crystals of
anhydrite, celestine,
gypsum and traces of dolomite
(AM 52.1332-1340).
At the Clear Creek claim, Goat Mountain, New Idria Mining District, San Benito county, California, USA, huntite has been found on
magnesite associated with gypsum
(Minrec 36.4.354).
At the Crestmore quarries, Crestmore, Riverside county, California, USA, the mineral assemblage magnesium
calcite-aragonite-huntite has been found as an
encrustation on brecciated
calcite-monticellite rock. The
magnesium-calcite-aragonite-huntite assemblage
was considered
to represent a metastable early mineral assemblage. In some places replacement by an equilibrium
dolomite-calcite assemblage was found
(AM 52.1332-1340).
At the Sierra Magnesite Mine, Gabbs, Gabbs Mining District, Nye county, Nevada, USA, early dolomite
has been mineralised and in part converted to magnesite; subsequent igneous activity has resulted
in brucite being developed. The huntite occurs as veinlets in the fractured and weathered
mantle of the brucite and is associated with
hydromagnesite. Surface waters percolating downwards are considered to have precipitated the
huntite
(AM 52.1332-1340).
At the type locality, the Ala-Mar deposit, Currant Mining District, White Pine county, Nevada, USA, huntite was deposited by cool
waters in cavities and vugs in rocks composed of magnesite,
dolomite and deweylite.
The magnesite deposits are directly overlain by dacite;
in parts the dacite is overlain by volcanic breccia,
which in turn is overlain by basaltic andesite.
The host rock of the magnesite and associated minerals is a bedded
tuff formation, which overlies the lower volcanics. The
tuff is overlain by latite.
The minerals of the tuff include
enstatite-ferrosilite,
augite, hornblende,
biotite, plagioclase,
sanidine, quartz,
apatite, magnetite and
calcite. Subsequent to deposition some of the tuff beds
were altered by cool meteoric waters. The volcanic glass was in part changed to montmorillonite
and there was some replacement by calcite. The magnesite
deposits were formed by hydrothermal solutions rich in magnesium and carbon dioxide which ascended along channelways provided by the fault
zones. Where calcite was present, the replacing solutions produced
dolomite until no more calcite was in actual contact with
the solution. Thereafter, the hydrothermal solutions replaced the tuff with
magnesite and deweylite.
In the magnesite deposit the early stage represents replacement of the
tuff by calcite and
montmorillonite.
Then magnesium-rich solutions react with the calcite of the
tuff to form dolomite and the solutions became
impoverished in calcium.
Then magnesite and later deweylite formed.
At the close of this stage calcite and silica minerals (quartz,
chalcedony and opal) were deposited along with some
dolomite and deweylite. Finally the silica minerals and
calcite were the sole phases forming. The solutions gradually cooled to the temperature of the ground
waters and calcite continued to form. During the late stage the vugs in the replaced rocks were
lined with botryoidal calcite. The last mineral to fill these cavities was huntite, which
occurs as a white powdery mass. Huntite is believed to have been precipitated as a very fine powder from cool ground waters which
gathered their magnesium locally in traversing the magnesite deposits
(AM 38.4-24).
At the Carlsbad Caverns, Carlsbad Caverns National Park, Eddy county, New Mexico, USA, huntite has been reported associated with
aragonite, calcite,
hydromagnesite and dolomite.
Aragonite, calcite and
hydromagnesite are precipitated directly from solution whereas
dolomite and huntite apparently are derived from the alteration of
hydromagnesite. It was concluded that huntite was a metastable mineral under the
cave conditions
(AM 52.1332-1340).
At the Kurgashinkan mine, Okhangaron District, Tashkent, Uzbekistan, huntite was formed as fracture fillings in the weathered mantle of
lightly serpentinised dolostone and was associated also with
hydromagnesite and opal. The
opal often penetrated the huntite in a network of line fractures, while
hydromagnesite occurred as very small crystals in cavities in the huntite. The
huntite was considered to result from supergene conditions connected with
circulation of surface waters rich in magnesium from traversing the local dolostone
(AM 52.1332-1340).
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