Sapphirine

sapphirine

spinel

enstatite

hercynite

Images

Formula: Mg₄(Mg₃Al₉O₄)[Si₃Al₉O₃₆]
Inosilicate (chain silicate), sapphirine group, sapphirine supergroup
Crystal System: Monoclinic
Specific gravity: 3.4 to 3.5 measured
Hardness: 7½
Streak: Colourless
Colour: Light blue, blue-gray, green, greenish gray, rarely yellow-brown or pink

Environments:

Plutonic igneous environments
Metamorphic environments

Sapphirine is found in high temperature metamorphic rocks or xenoliths with abundant aluminium and magnesium and low silicon. It may occur as a primary magmatic mineral
It is a mineral of the granulite facies.

Alteration

anorthite, enstatite, spinel, K₂O and H₂O to Al-rich hornblende, Mg-rich sapphirine and phlogopite
2.5Ca(Al₂Si₂O₈) + 10MgSiO₃ + 6MgAl₂O₄ + K₂O + 3H₂O → Ca_2.5Mg₄Al(Al₂Si₆)O₂₂(OH)₂ + 3Mg₂Al₄SiO₁₀ + 2KMg₃(AlSi₃O₁₀)(OH)₂
This reaction occurs in the granulite to amphibolite facies (DHZ 2A p631).

Al-rich hornblende, spinel, quartz, K₂O and H₂O to anorthite, Mg-rich sapphirine and phlogopite
Ca_2.5Mg₄Al(Al₂Si₆)O₂₂(OH)₂ + 4 MgAl₂O₄ + 6SiO₂ + K₂O + H₂O → 2.5Ca(Al₂Si₂O₈) + Mg₂Al₄SiO₁₀ + 2KMg₃(AlSi₃O₁₀)(OH)₂
(DHZ 2A p631)

spinel-hercynite, sillimanite and quartz to sapphirine
7(Mg,Fe²⁺)Al₂O₄ + 2Al₂SiO₅ + SiO₂ → 4(Mg,Fe)_1.75Al_4.5Si_0.75O₁₀
(DHZ 2A p633)

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