Jadeite

inosilicate

metamorphic

Formula:NaAlSi2O6
Inosilicate (chain silicate), pyroxene group
Specific gravity: 3.25 to 3.35
Hardness: 6
Streak: White
Colour: apple-green, greenish white, purplish blue, blue-green
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Metamorphic environments

Jadeite is found only in metamorphic rocks. It is a characteristic mineral of the blueschist facies, where it may be associated with glaucophane.

Alteration

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO2 and H2O
8Na(AlSi3O8) + (Mg4.0Fe2.0)(AlSi3O10)(OH)8 + CaCO3 → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 2SiO2 + CO2 + 2H2O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above (DHZ 2A p475).

albite and montmorillonite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz and H2O
8Na(AlSi3O8) + 2Ca0.5(Mg3.5Al0.5)Si8O20(OH)4.nH2O → 5(Na0.8Ca0.2)(Mg0.2Al0.8Si2)6 + 2Na2(Mg3Al2)(Al0.5Si7.5)O22(OH)2 + 15SiO2 +6H2O
This reaction occurs in low to intermediate metatmorphism (DHZ 2A p 475).

analcime to jadeite and H2O
Na(AlSi2O6).H2O → NaAlSi2O6 + H2O
At high temperature analcime changes to jadeite (ZW)

anorthite, albite and H2O to jadeite, lawsonite and quartz
CaAl2 Si2O8 + NaAlSi3O8 + 2H2O → NaAlSi2O6 + CaAl2(Si2O7)(OH)2.H2 + SiO2
(DHZ 2A p475)

jadeite to nepheline and albite
2NaAlSi2O6 ⇌ NaAlSiO4 + NaAlSi3O8
At 20 kbar pressure the equilibrium temperature is about 1,000oC (eclogite facies), with equilibrium to the right at higher temperatures and to the left at lower temperatures (Minsoc Amer sp pap 2, 151-161 (1969)).

jadeite, diopside, magnetite and quartz to aegirine, kushiroite (pyroxene) and hypersthene
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).

jadeite and quartz to albite
NaAlSi2O6 + SiO2 ⇌ NaAlSi3O8
High pressure favours the reverse reaction. Sometimes found in blueschist metamorphic rocks. (KB p209)
The equilibrium temperature for this reaction at 10 kbar pressure is about 400oC (blueschist facies), and at 26 kbar the equilibrium temperature is 1,000oC (eclogite facies). For any given pressure the equilibrium is to the right at higher temperatures, and to the left at lower temperatures, and for any given temperature the equilibrium is to the left at higher pressures and to the right at lower pressures (Tulane, Presnall).

lawsonite and jadeite to clinozoisite, paragonite, SiO2 and H2O
4CaAl2(Si2O7)(OH)2.H2 + 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).

Common impurities: Ti,Mn,Mg,Ca,K,H2O

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