Wairakite

wairakite

zoisite

margarite

lawsonite

Images

Formula: Ca(Si₄Al₂)O₁₂.2H₂O
Tectosilicate (framework silicate) zeolite group
A complete series between wairakite and analcime exists.
Crystal System: Monoclinic
Specific gravity: 2.26 measured, 2.272 calculated
Hardness: 5½ to 6
Streak: White
Colour: Colourless, white
Common impurities: Fe,Mg,Sr,Na,K,Cs
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 300^oC, at a depth of 72 to 1600 metres. It is stable above 210^oC, 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).

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