Wairakite

tectosilicate

analcime

Formula: Ca(Si4Al2)O12.2H2O
Tectosilicate (framework silicate) zeolite group
A complete series between wairakite and analcime exists.
Specific gravity: 2.26
Hardness: 5½ to 6
Streak: White
Colour: Colourless, white
Environments:

Volcanic igneous environments
Metamorphic environments
Hydrothermal environments
Geothermal wells

In Iceland wairakite occurs in metamorphosed volcanics and the deepest and hottest geothermal wells, with temperatures up to 300oC, at a depth of 72 to 1600 metres. It is stable above 210oC, but at cooler temperatures laumontite forms instead. Its formation also depends on the concentration of aqueous CO2. If this is too high calcite forms instead of wairakite (AofA).

At the Wairake Geothermal Field, Taupo, Central North Island, New Zealend, wairakite was discovered in drill cores in hydrothermally altered
rhyolite (AJM 19.2.33).

Alteration

lawsonite to margarite, zoisite, wairakite and H2O
6CaAl2(Si2O7(OH)2.H2O ⇌ CaAl2Si2Al2O10(OH)2 + 2Ca2Al3[Si2O7][SiO4]O(OH) + Ca(Si4Al2)O10.2H2O + 8H2O
Increasing temperature favours the forward reaction (AM61.699-709).

lawsonite and kaolinite to margarite and wairakite and H2O
2CaAl2(Si2O7(OH)2.H2O + Al2Si2O5(OH)4 ⇌ CaAl2Si2Al2O10(OH)2 + Ca(Si4Al2)O10.2H2O + 3H2O
Increasing temperature favours the forward reaction (AM61.699-709).

lawsonite and quartz to wairakite
CaAl2(Si2O7(OH)2.H2O + 2SiO2 ⇌ Ca(Si4Al2)O10.2H2O
Increasing temperature favours the forward reaction (AM61.699-709).

wairakite to anorthite and quartz and H2O
Ca(Si4Al2)O10.2H2O ⇌ Ca(Al2Si2O8) + 2SiO2 + 2H2O
Increasing temperature favours the forward reaction (AM61.699-709).

wairakite to zoisite and margarite and quartz and H2O
5Ca(Si4Al2)O10.2H2O ⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + CaAl2Si2Al2O10(OH)2 + 12SiO2 + 8H2O
Increasing temperature favours the forward reaction (AM61.699-709).

wairakite and kaolinite to margarite and quartz and H2O
Ca(Si4Al2)O10.2H2O + Al2Si2O5(OH)4 ⇌ CaAl2Si2Al2O10(OH)2 + 4SiO2 + 3H2O
Increasing temperature favours the forward reaction (AM61.699-709).

wairakite and pyrophyllite to margarite, quartz and H2O
Ca(Si4Al212.2H2O + Al2Si4O10(OH)2 ⇌ CaAl2Si2Al2O10(OH)2 + 6SiO2 + 2H2O
Increasing temperature favours the forward reaction (SERC).

wairakite, zoisite and margarite to anorthite and H2O
Ca(Si4Al2)O10.2H2O + 2Ca2Al3[Si2O7][SiO4]O(OH) + CaAl2Si2Al2O10(OH)2 ⇌ Ca(Al2Si2O8) + H2O
Increasing temperature favours the forward reaction (AM61.699-709).

Common impurities: Fe,Mg,Sr,Na,K,Cs

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