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Formula: KCa4Si8O20(OH,F).8H2O
Phyllosilicate (sheet silicate), apophyllite group, forms a series with
fluorapophyllite-(K)
Crystal System: Tetragonal
Specific gravity: 2.37 measured, 2.36 clculated
Hardness: 4 to 5
Streak: White
Colour: White, pink, green, yellow, violet. The green colour of some apophyllite
has been attributed to vanadium Dana
Common impurities: Al,Na
Environments
Plutonic igneous environments
Metamorphic environments
Hydrothermal environments
Basaltic cavities
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. Please check the apophyllite page for more information.
Hydroxyapophyllite-(K) is found chiefly as a late mineral in amygdules and druses in
basalt, where it is associated with
fluorapophyllite, datolite,
pectolite, calcite and
zeolites. Less frequently found in cavities in
granite and syenite, in
metamorphic rocks and limestone and
calc-silicate rock, sometimes as an alteration of
wollastonite, and as a late product in hydrothermal ore deposits
(Dana, HOM).
Localities
In India all of the specimens from the major part of the Deccan basalts have
been found on analysis to be fluorapophyllite, whereas those from the
albite-rich basalts of Mumbai have
been found to be hydroxylapophyllite-(K)
(Minrec 34.1.30).
At Guanajuato, Guanajuato Municipality, Guanajuato, Mexico, many excellent hydroxyapophyllite-(K) exhibit specimens
have been found
(AM 63.196-202).
At the type locality, the Ore Knob mine, Ore Knob, Ashe county, North Carolina, USA, hydroxyapophyllite-(K) occurs as
a 1.0 cm coating of multiply-twinned white crystals on a pyrrhotite and
chalcopyrite ore
(HOM).
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