Merwinite

nesosilicate

marble

Formula: Ca3Mg(SiO4)2 nesosilicate (insular SiO4 groups)
Specific gravity: 3.15 to 3.32
Hardness: 6
Streak: White
Colour: White, colourless, light green, light gray green

Metamorphic environments

At the type locality merwinite is found in high temperature, low pressure contact metamorphic zones with marbles; in siliceous dolomitic limestone in contact metamorphic zones, it is formed at relatively elevated temperatures.

Alteration

monticellite and spurrite to merwinite and calcite
2CaMg(SiO4) + Ca5(SiO4)2(CO3) ⇌ 2Ca3Mg(SiO4)2 + CaCO3

monticellite, spurrite and quartz to merwinite and CO2
5CaMg(SiO4) + Ca5(SiO4)2(CO3) + SiO2 ⇌ 5Ca3Mg(SiO4)2 + 2CO2

Common impurities: Al, Fe

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