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Formula: NaCa4Si8O20F.8H2O
Phyllosilicate (sheet silicate), apophyllite group
Crystal System: Orthorhombic
Specific gravity: 2.50 measured, 2.30 calculated
Hardness: 4 to 5
Streak: White
Colour: Brownish-yellow, yellowish-brown, colourless
Solubility: Dissolved by hydrochloric acid with separation of silica (Dana, as natroapophyllite)
Common impurities: K
Environments
Igneous environments
Metamorphic environments
Hydrothermal environments
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.
Fluorapophyllite-(Na) occurs as a secondary mineral in
amygdules or druses in basalt, in cavities in
granite, in tactite
and other
metamorphic rocks, and as a late-stage hydrothermal mineral in some mineral deposits. Associated minerals include
zeolites, datolite,
pectolite, calcite and
quartz
(HOM).
Localities
At the type locality, the Sampo mine, Shitouyouze, Bicchu-cho, Takahashi City, Okayama Prefecture, Japan,
fluorapophyllite-(Na) occurs in skarn as prismatic crystals
alternately
zoned with fluorapophyllite, and associated with
zeophyllite, cuspidine and
calcite
(AM 66.416-423, Dana, as natroapophyllite).
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