Formula: NaAl2(Si3Al)O10(OH)2
Phyllosilicate (sheet silicate), mica group
Specific gravity: 2.78
Hardness: 2½
Streak: White
Colour: Colourless, pale yellow
Solubility: Insoluble in water and hydrochloric acid
Environments:
Sedimentary environments
Metamorphic environments
Paragonite is a metamorphic mineral formed under a broad range of pressure-temperature
conditions, sometimes associated with kyanite and
staurolite. It may also be found as detrital and authigenic
(formed in place) sediments
(DHZ 3 pps 9, 34).
Paragonite is a common constituent of
eclogite.
It is also found in phyllite,
schist and
gneiss.
It is a mineral of the greenschist and
blueschist facies.
Alteration
amphibole, chlorite, paragonite,
ilmenite, quartz and
calcite to garnet,
omphacite, rutile, H2O
and CO2
NaCa2(Fe2Mg3)(AlSi7)O22(OH)2 +
Mg5Al(AlSi3O10)(OH)8 +
3NaAl2(Si3Al)O10(OH)2 + 4Fe2+Ti4+O3 +
9SiO2 + 4CaCO3 →
2(CaMg2Fe3)Al4(SiO4)6 +
4NaCaMgAl(Si2O6)2 + 4TiO2 + 8H2O +
4CO2
In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to
reactions such as the above
(DHZ 2A p453).
lawsonite and jadeite to
clinozoisite, paragonite, quartz
and H2O
4CaAl2(Si2O7)(OH)2.H2O + NaAlSi2O6
⇌ 2Ca2Al3[Si2o7][SiO4]O(OH) +
NaAl2(Si3Al)O10(OH)2 + SiO2 +6H2
Clinozoisite and paragonite may have been derived from
lawsonite by the above reaction
(DHZ 2A p477).
paragonite and quartz to
albite and andalusite and H2O
NaAl2(Si3Al)O10(OH)2 + SiO2 ⇌ Na(AlSi3O8) +
Al2OSiO4 + H2O
Increasing temperature favours the forward reaction
(AM61.699-709).
paragonite and quartz to
albite, kyanite and H2O
NaAl2(Si3Al)O10(OH)2 + SiO2 ⇌ Na(AlSi3O8) +
Al2OSiO4 + H2O
Increasing temperature favours the forward reaction
(AM61.699-709).
Back to Minerals