You may ask "How can a rock change?"
All minerals are stable only within certain ranges of pressure and temperature. An igneous rock may have crystallized out of a very high temperature environment, and when that environment changes the minerals in the rock are no longer stable. Then the minerals evolve (over a period of hundreds of years) into something else. Small grey calcite crystals in limestone, for example, turn into large white crystals in marble. Or the rock may undergo a solid state reaction with the stone and air around it.
When the temperature and pressure change sufficiently to allow phase changes or chemical reactions that weren't allowed at the time a rock was originally formed, a new rock may be formed from a reassemblage of the minerals that were originally present. Such temperature and pressure changes come about naturally during the folding process. Thus metamorphic rocks generally have the same mineralogic compostition as igneous rock composed of feldspar, mica,
Go to a listing of Rocks by mineral group
You may ask "How can a rock change?"
All minerals are slightly unstable and may change their "state" (over a period of hundreds of years) depending upon changes in the temperature and pressure of their surroundings. An igneous rock may have crystallized out of a very high temperature magma, and when that environment changes, the minerals in the rock are no longer stable. Then the minerals evolve into something else. Small grey calcite crystals in limestone, for example, turn into large white crystals in marble.
When the temperature and pressure change sufficiently to allow phase changes or chemical reactions that weren't allowed at the time a rock was originally formed, a new rock may be formed from a reassemblage of the minerals that were originally present. Such temperature and pressure changes come about naturally during the folding process. Thus metamorphic rocks generally have the same mineralogic compostition as igneous rock composed of feldspar, mica, olivine, pyroxene, and the like.
Go to a listing of Rocks by mineral group
Not applicable at this reading level.
Go to a listing of Rocks by mineral group
