Gehlenite

gehlenite

grossular

spurrite

merwinite

Images

Formula: Ca2Al(SiAl)O7
Sorosilicate (Si2O7 groups), melilite group
Specific gravity: 2.9 to 3.06
Hardness: 5 to 6
Streak: white, greyish white
Colour: colourless, greenish grey, yellowish brown
Solubility: Insoluble in water; soluble in hydrochloric acid forming an insoluble silica gel
Common impurities: Ti,Fe,Mg,Mn,Na,K
Environments:

Metamorphic environments

Gehlenite is a contact metamorphic mineral in limestone; it is a mineral of the granulite facies. It also occurs in calcium-rich ultramafic volcanic rocks. Associated minerals include dolomite, calcite, augite, olivine, nepheline, leucite, merwinite, spurrite, diopside, ferroan spinel, phlogopite, pyrope, grossular, antigorite, pyroxenes, apatite and vesuvianite (HOM).

Localities

The type locality is the Monzoni Mountains, Trento Province, Trentino-Alto Adige, Italy.

Alteration

grossular to anorthite, gehlenite and wollastonite
2Ca3Al2(SiO4)3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7 + 3CaSiO3
The equilibrium temperature for this reaction at 5 kbar pressure is 1,110oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures (SERC).

grossular and corundum to anorthite and gehlenite
2Ca3Al2(SiO4)3 + Al2O3 ⇌ CaAl2Si2O8 + Ca2Al2SiO7
The equilibrium temperature for this reaction at 5 kbar pressure is about 950oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures (SERC).

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