Paragonite

paragonite

ilmenite

lawsonite

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Formula: NaAl2(Si3Al)O10(OH)2
Phyllosilicate (sheet silicate), dioctahedral mica group of the mica group, forms a series with muscovite
Crystal System: Monoclinic
Specific gravity: 2.85 measured, 2.907 calculated
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.

Associated minerals include kyanite, staurolite, muscovite, quartz, glaucophane, chlorite, garnet, tourmaline, calcite and actinolite (HOM).

Localities

At the type locality, Sponda Alp - Pizzo Forno, Chironico Valley, Faido, Leventina, Ticino, Switzerland, paragonite occurs as a talc-like mineral in metamorphic schist and phyllite. Associated Minerals include staurolite, quartz and muscovite (Mindat).

Alteration

Regardless of a rock’s bulk composition or mineral assemblage, an increase in metamorphic pressure leads to an increase in the Fe, Mg, and Si contents of muscovite, ie in the solid solution toward celadonite. In contrast, the composition of paragonite is largely unaffected by increasing pressure (CM 38.707-712).

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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