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Formula:NaFe3+Si2O6
Inosilicate (chain silicate), clinopyroxene
Crystal System: Monoclinic
Specific gravity: 3.5 to 3.6 measured, 3.576 calculated
Hardness: 6
Streak: Pale yellowish grey
Colour: Black, brown, green. Bright green to yellow-green in thin section.
Solubility: Aegirine is slightly soluble in hydrochloric acid.
Common impurities: Al,Ti,V,Mn,Mg,Ca,K,Zr,Ce
Environments:
Plutonic igneous environments
Pegmatites
Carbonatites
Metamorphic environments
Aegirine is a pyroxene. It is a relatively rare
primary mineral found chiefly
in igneous rocks rich in sodium and poor in SiO2 and in
syenite
pegmatites. It is also found as a
secondary mineral in metamorphic rocks.
Aegirine may be found in
granite,
syenite,
nepheline syenite,
rhyolite and
schist.
In igneous rocks it is associated with orthoclase,
feldspathoids,
augite and soda-rich amphibole.
In hornfels of
contact metamorphic rocks it is found with
quartz,
spessartine and riebeckite.
Alteration
aegirine and CaO to andradite, quartz and
Na2O
2NaFe3+Si2O6 + 3CaO →
Ca3Fe3+2 (SiO4)3 + SiO2 + Na2O
This is a high temperature process
(DHZ 2A p508).
aegirine, epidote and CO2 to
albite, hematite,
quartz,
calcite and H2O
4NaFe3+Si2O6 +
2Ca2(Al2Fe3+ [Si2O7](SiO4)O(OH) + 4CO2
→ 4Na(AlSi3O8) + 3Fe2O3 + 2SiO2 + 4CaCO3 +
H2O
(DHZ 2A p511)
albite, diopside and
magnetite to aegirine, Si2O6,
garnet and quartz
2Na(AlSi3O8) + CaMgSi2O6 +
Fe2+Fe3+2O4 ⇌ 2NaFe3+Si2O6 +
Si2O6 + CaMgFe2+Al2(SiO4)3 + SiO2
This reaction may occur in blueschist facies rocks in Japan
(DHZ 2A p512).
serpentine, aegirine and
quartz to magnesio-riebeckite
and H2O
Mg3Si2O5(OH)4 + 2NaFe3+Si2O6 +
2SiO2 →
Na2 (Mg3Fe3+2)Si8O22(OH)2 +
H2O
(DHZ 2A p511)
titanomagnetite (ilmenite combined with magnetite),
quartz, and
aegirine-hedenbergite to
aenigmatite, hedenbergite,
magnetite and O2
6(Fe2+Ti4+O3 + Fe2+Fe3+2O4) +
12SiO2 + 12(NaFe3+Si2O6 + CaFe2+Si2O6)
⇌
3Na4[Fe2+10Ti2]O4[Si12O36] +
12CaFe2+Si2O6 + 2Fe2+Fe3+2O4 +
5O2
(DHZ 2A p652)
jadeite, diopside,
magnetite and quartz to aegirine,
kushiroite (pyroxene) and
enstatite-ferrosilite
2NaAlSi2O6 + CaMgSi2O6 +
Fe2+Fe3+2O4 + SiO2 ⇌
2NaFe3+Si2O6 + CaAlAlSiO6 + MgFeSi2O6
Aegirine in blueschist facies rocks may be formed
by the above reaction.
(DHZ 2A 512)
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