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Formula: ☐Mg2Mg5Si8O22(OH)2
Inosilicate (chain silicate),
magnesium-iron-manganese amphibole subgroup,
amphibole supergroup
Anthophyllite is a paramorph of
cummingtonite.
Crystal System: Orthorhombic
Specific gravity: 2.85 to 3.57 measured, 3.67 calculated
Hardness: 5½
Streak: White
Colour: Brownish, yellowish grey
Solubility: Insoluble in hydrochloric, sulphuric or nitric acid
Common impurities: Ti,Al,Mn,Ca,Na
Environments:
Anthophyllite is a metamorphic product of magnesium-rich rocks such as
ultramafic igneous rocks and impure
dolomite shale.
It is common in cordierite-bearing
gneiss and schist. It may
also form as a retrograde product rimming relict
orthopyroxenes such as
enstatite and
olivine.
Anthophyllite may be found in
gneiss and
schist.
It is a mineral of the
hornblende-hornfels facies.
Localities
The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia,
are skarn deposits at the contact between
granodiorite and volcanic rocks.
Anthophyllite is a primary silicate that occurs rarely
with actinolite and hornblende
in the skarn
(AJM 22.1.33).
Alteration
anthophyllite to enstatite, quartz and H2O
2☐Mg2Mg5Si8O22(OH)2 ⇌
7Mg2Si2O6 + 2SiO2 + 2H2O
At 10 kbar pressure the equilibrium temperature is about 810oC
(granulite facies). The equilibrium moves to the right at
higher temperatures and to the left at lower temperatures
(SERC).
anthophyllite and forsterite to enstatite
and H2O
2☐Mg2Mg5Si8O22(OH)2 + 2Mg2SiO4 ⇌
9Mg2Si2O6 + 2H2O
At 2 kbar pressure the equilibrium temperature is about 690oC
(pyroxene-hornfels facies). The equilibrium moves
to the right at
higher temperatures and to the left at lower temperatures
(SERC).
forsterite and talc to anthophyllite
and H2O
4Mg2SiO4 + 9Mg3Si4O10(OH)2 ⇌
5Mg2Mg5Si8O22(OH)2 + 4H2O
At 2 kbar pressure the equilibrium temperature is about 650oC
(pyroxene-hornfels facies), with equilibrium
to the right at
higher temperatures and to the left at lower temperatures (for the same pressure)
(DHZ 1A p258, SERC).
talc to anthophyllite,
quartz and H2O
7Mg3Si4O10(OH)2 ⇌
3☐Mg2Mg5Si8O22(OH)2 + 4SiO2 + 4H2O
At 10 kbar pressure the equilibrium temperature is about 790oC
(granulite facies). The equilibrium moves to the right at
higher temperatures and to the left at lower temperatures
(http://www.tulane.edu/~sanelson/eens212/metaminerals.htm, SERC).
talc and enstatite to anthophyllite
Mg3Si4O10(OH)2 + 2Mg2Si2O6 →
☐Mg2Mg5Si8O22(OH)2
At 10 kbar pressure the equilibrium temperature is 750oC
granulite facies.
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