pressure and temperature.
pressure: eg. regional metamorphism
take a limestone and squeeze the hell out of it, the crystals realign and you'll get marble.
heat: eg. contact aureoles
take a limestone and have a melt intrude into it. the crystals in the border zone realign and you'll get marble
pressure: eg. regional metamorphism
take a limestone and squeeze the hell out of it, the crystals realign and you'll get marble.
heat: eg. contact aureoles
take a limestone and have a melt intrude into it. the crystals in the border zone realign and you'll get marble
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due to the change in tempreature and pressure on the pre existing ignrous ,sedimentary and even metamorphic rocks the chemical composition changes and the rock changes into an metamorphic rock