1. Mineral Reactions
Mineral reactions are the basis for much of our understanding of metamorphism.
Our estimates of pressures and temperatures experienced by rocks during metamorphism are based on metamorphic reactions.

2. Mineral Reactions There are two basic types of mineral reactions:
Continuous
Discontinuous

3. Discontinuous Reactions
(after Liou, 1987)
Minerals that are the products of reaction are different from the reactants
Ex: Albite -> Jadeite + Quartz NaAlSi3O8 -> NaAlSi2O6 + SiO2
Jadeite and Quartz are different from Albite
Generally make good geobarometers because they have a gentle slope on a P-T graph

4. (after Liou, 1987)
Albite -> Jadeite + Quartz Geobarometer A good geobarometer has a gentle slope

5. Continuous Reactions
Minerals that are the products of reaction are the same as the reactants. Elements are exchanged between different minerals
Ex: Fe-Mg exchange between garnet and pyroxene
Fe-garnet Mg-pyroxene -> Mg-garnet + Fe-pyroxene
Fe3Al2Si3O12 + 3CaMgSi2O6 -> Mg3Al2Si3O12 + 3CaFeSi2O6
Generally make good geothermometers

6. Garnet-clinopyroxene geothermometer
A good geothermometer has a steep slope
after Krogh Ravna 2000