Images
Formula: Ca2MgSi2O7
Sorosilicate (Si2O7 groups), melilite group,
forms a series with gehlenite
Near end-member åkermanite is very rare, possibly unknown in nature.
Crystal System: Tetragonal
Specific gravity: 2.944 measured, 2.922 calculated
Hardness: 5 to 6
Streak: White
Colour: Colourless, grey, green, brown
Melting point: 1,454oC at a pressure of 1 kbar
Environments:
Plutonic igneous environments
Metamorphic environments
Commonly found in slags. Åkermanite is a product of contact
metamorphism of
siliceous limestone and
dolostone, and it also forms from alkalic magmas rich in calcium.
(Mindat).
It is a common component of
skarn, and a mineral of the
sanidinite and
granulite facies.
Common associates include diopside,
forsterite, larnite,
merwinite, monticellite,
spurrite and wollastonite
(Mindat).
Alteration
As åkermanite cools from its melting point it is stable down to 1345oC, when the stable mixture is
åkermanite and wollastonite. From 1240oC down to
1050oC a mixture of åkermanite, wollastonite and
diopside is stable, and at lower temperatures åkermanite dissociates to form
wollastonite and monticellite.
The stability of åkermanite is limited to pressures of less than 14 kbar in an anhydrous environment, and less than 10.2
kbar with excess H2O
(DHZ 1B p307).
åkermanite to wollastonite and
monticellite
Ca2MgSi2O7 ⇌ CaSiO3 + CaMgSiO4
The forward reaction occurs at temperature less than 1,050oC
(DHZ 1B p307)
åkermanite and CO2 to diopside and
calcite
Ca2MgSi2O7 +
CO2 ⇌ CaMgSi2O6 + CaCO3
The maximum stability limit of åkermanite in the presence of excess CO2 is about 6 kbar. Below that
pressure, at relatively lower temperatures, åkermanite reacts with CO2 to form
diopside and calcite
according to the above reaction
(JVW p144).
diopside and
monticellite to åkermanite and
forsterite
CaMgSi2O6 + 3CaMgSiO4 ⇌ 2Ca2MgSi2O7
+ Mg2SiO4
(DHZ 1B p313)
monticellite and CO2 to
åkermanite, forsterite and
calcite
3CaMgSiO4 + CO2 ⇌ Ca2MgSi2O7 +
Mg2O7 + CaCO3
At 4.3 kbar pressure the equilibrium temperature is about 890oC
(granulite facies)
(DHZ 1A p357).
monticellite and diopside to
åkermanite and forsterite
3CaMgSiO4 + CaMgSi2O6 ⇌ 2Ca2MgSi27 +
Mg2O7
Monticellite is stable below 890oC at pressure of about 4.3 kbar
(granulite facies).
DHZ 1A p357)
nepheline and diopside to åkermanite,
forsterite and albite
3NaAlSiO4 + 8CaMgSi2O6 ⇌ 4Ca2MgSi2O7 +
2Mg2SiO4 + 3NaAlSi3O8
This reaction is in equilibrium at about 1180oC, with lower temperatures favouring the forward reaction
(DHZ 4 p251).
Back to Minerals