Paragonite

muscovite

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).

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