Gehlenite

sorosilicate

metamorphic

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
Environments:

Metamorphic environments

Gehlenite is a contact metamorphic mineral in limestone. It is a mineral of the granulite facies.

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).

Common impurities: Ti,Fe,Mg,Mn,Na,K

Back to Minerals