Images
Formula: NaAl2(Si3Al)O10(OH)2
Phyllosilicate (sheet silicate),
dioctahedral mica group of the
mica group, forms a series with
muscovite
Brammallite is a sodium-deficient variety of paragonite.
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).
Back to Minerals