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Apophyllite refers to a five minerals:
Fluorapophyllite-(Cs)
Cs4Si8O20F.8H2O
Fluorapophyllite-(K)
KCa4Si8O20F.8H2O
Fluorapophyllite-(Na)
NaCa4Si8O20F.8H2O
Fluorapophyllite-(NH4)
NH4Ca4Si8O20F.8H2O
Hydroxyapophyllite-(K)
KCa4Si8O20(OH,F).8H2O
They are all phyllosilicates (sheet silicates)
Specific gravity: 2.3 to 2.4
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, yellow, green, brown, pink
Solubility: Moderately soluble in hydrochloric acid
Environments:
Plutonic igneous environments
Metamorphic environments
Hydrothermal environments
Basaltic cavities most common
Historically all the apophyllite group minerals were reported
simply as
"apophyllite", and indeed it requires analysis to
differentiate between them, so there is comparatively little information about the individual members of the group, except in
recent times.
As a general rule, both fluorapophyllite and hydroxyapophyllite may be present on a single specimen, and
frequently are. Aside from Jefferson, North Carolina, and Kimberley, South Africa, only one other locality provides specimens
which consistently have OH > F. This locality is Guanajuato, Mexico, which has provided many excellent hydroxyapophyllite
exhibit specimens
(AM 63.196-202).
Apophyllite occurs chiefly as a late secondary mineral in
amygdules and druses in basalt, associated with
zeolites (such as stilbite,
heulandite,
chabazite),
datolite,
calcite and pectolite. It is found
less frequently in cavities in granite and
syenite, in metamorphic
rocks and limestone and
calc-silicate rocks,
sometimes as an alteration of wollastonite, and as a late product in
hydrothermal ore deposits
(Dana, HOM).
Localities
At the Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in
veins of hydrothermal origin in skarn.
Apophyllite occurs as colourless and transparent crystals reaching 3 cm in length. Associated minerals include
andradite, diopside,
hedenbergite, calcite and
olshanskyite, and apophyllite is the last to crystallise in the
paragenesis
(R&M 96.5.398).
Apophyllite from the Shijiangshan Mine -
Image
In the Deccan traps, India, in most localities apophyllite crystallised later than
heulandite, and at the same time as, or shortly following,
stilbite. Rarely, second generation apophyllite has been found
(Minrec 34.1.30-36).
At Rahuri, Ahmednagar District, Maharashtra, India, a find in 2000 produced many very large green apophyllite
crystals with flat pinacoid terminations and very small pyramid faces, arranged in discrete hemispherical groups on beds
of white stilbite crystals
(Minrec 34.1.30).
Apophyllite from Rahuri - Image
At Savada, Dharangaon Taluka, Jalgaon District, Maharashtra, India, apophyllite occurs in hard, nearly impermeable
basalt, almost wholly without channels connecting the cavities. Hence
neighbouring cavities often display very different
mineralisation. The apophyllite is sometimes colourless, and only very rarely deep green, attributable to
inclusions of celadonite and related phyllosilicates
(Minrec 34.1.30-36).
At the Pune District, Maharashtra, India, in several locations fine crystals of apophyllite are found, coloured
green by vanadium V5+, with the intensity of the colour increasing
proportionately to the vanadium content.
Crystals are usually well formed and exhibit faces {110} (prism), {101} (pyramid) and {001} (pinacoid).
In the Pashan quarries the crystals have formed in basalt with particularly
large cavities that are widely interconnected so that uniform solutions
circulated among them
(Minrec 34.1.30-36).
Apophyllite from Pashan, Pune District -
Image
In a quarry in Mahad, Raigad District, Maharashtra, India, pseudomorphs of
calcite and fluorite after
apophyllite were found
(Minrec 34.1.30-36).
Apophyllite from Mahad - Image
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).
Apophyllite specimens from Charcas are not common. The crystals are lightly cloudy to transparent and colourless
to pink. They can reach 4 cm in length but are generally below 1 cm. They may be found resting on
calcite, danburite or
datolite, indicating a late stage of deposition. Pink apophyllite
reported from the Aurora mine generally consists of glassy-looking crystals on
danburite
(Minrec 55.6.732).
Apophyllite from the Aurora Mine, Charcas -
Image
At Low Knott Quarry, Forest in Teesdale, County Durham, England, UK, apophyllite crystals up to 1 cm long embedded
in calcite have been found in a 2 cm wide
calcite-quartz vein in
dolerite
(JRS 21.7).
At Cambokeels mine, Westgate, Stanhope, County Durham, England, UK, apophyllite crystals up to 7 mm were found in
abundance, typically accompanied by analcime crystals. In a few specimens the
apophyllite was overgrown by
pectolite. The apophyllite is probably fluorapophyllite-(K)
(JRS 21.7).
Fluorapophyllite-(K) from the Cambokeels Mine -
Image
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