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Formula: Fe2+8Si6O15(OH)10
Phyllosilicate (sheet silicate), pyrosmalite group, forms a
series with
pyrosmalite-(Mn)
Specific gravity: 3.06 to 3.19
Hardness: 4½
Streak: Light green
Colour: Yellow-green to tan, rarely pinkish. Surface often grey, dark green or brown due to alteration Dana. Colourless in transmitted light
(Webmin)
Common impurities: Al,Mg
Environments
Pyrosmalite-(Fe) occurs intergrown with sulphides, formed during metamorphism of a stratiform
lead-zinc deposit, and as a retrograde
reaction product derived from clinopyroxene in saline fluid inclusions in
contact metamorphic rocks.
Associated minerals include fayalite, greenalite,
galena, sphalerite,
clinopyroxene, hornblende,
grunerite, garnet,
biotite, magnetite and
apatite
(HOM).
Localities
Pyrosmalite-(Fe) occurs in the sulphide-rich central part of the Pegmont stratiform
lead-zinc deposit, 175 km southeast of Mount Isa,
Queensland, Australia, and probably formed during prograde metamorphism
(AM 73.933-934).
The type locality is the Bjelke mine, Nordmark Odal Field, Filipstad, Värmland County, Sweden.
Alteration
Pyrosmalite-(Fe) has been found in saline inclusions in magmatic quartz from altered
granodiorite. On heating above 450oC with a Ca-enriched saline inclusion
fluid, it reacts to form clinopyroxene. This suggests that
clinopyroxene was originally present in the inclusions at high temperature, and then underwent
retrograde reaction with the saline fluid, on cooling, to form pyrosmalite-(Fe). In its simplest form, the equilibrium reaction for
this transformation is:
Chlorine-rich pyrosmalite-(Fe) and Ca2+ to hedenbergite
(a clinopyroxene), Fe2+, Cl- and water
Fe8Si6O15[(OH)6Cl4] + 3Ca2+ (aq) = 3CaFeSi2O6 +
5Fe2+ (aq) + 4Cl– (aq) + 3H2O
(AM 88.151-158)
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