Metamorphic Rock. Rock Cycle. Metamorphism means "changed form". Agents of Metamorphism Changes occur because of: Heat Pressure Chemical fluids *Rocks adjust to become more stable under new, higher temperatures and pressures. HEAT
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Agents of Metamorphism
Changes occur because of:
*Rocks adjust to become more stable under new, higher temperatures and pressures.
Buried rocks are subjected to the force, or stress, Pressure (stress)as metamorphic agent exerted by the load above. This confining pressure is analogous to water pressure where the force is applied equally in all directions.
2. Tectonic pressures associated with convergent plate boundaries and continental collision also cause Regional Metamorphism.
Pressure along fault zones causes Dynamic Metamorphism, due to the crushing and ductile flow of rock.
In some metamorphic settings, new materials are introduced by the action of hydrothermal solutions (hot water with dissolved ions). Many metallic ore deposits form in this way.
Black smokers - Sea water percolates through newly formed oceanic crust, dissolving out metallic sulfide minerals.
The hot sea water rises along fractures and pours from vents in the seafloor as black clouds of dark mineral-rich water pour from the vent.
Sulfide minerals (such as pyrite, sphalerite, and galena) and copper precipitate when the hot water comes in contact with cold sea water.
(sediment) (sedimentary rock) (metamorphic)
Growth of new crystals.
No changes in overall chemistry.
New crystals grow from the minerals already present.
A preferred orientation of minerals commonly develops under applied pressure. Platy or sheet-like minerals such as muscovite and biotite become oriented perpendicular to the direction of force. This preferred orientation is called foliation.
A texture of this sort in a metamorphic rock is called FOLIATION and the rocks are said to be FOLIATED.
Phyllite - fine-grained metamorphic rock. Has a frosted sheen, resembling frosted eye shadow. This is no coincidence.
Gneiss - (pronounced "nice") - a banded or striped rock with alternating layers of dark and light minerals. The dark layers commonly contain biotite, and the light layers commonly contain quartz and feldspar.
Schist - metamorphic rock containing abundant obvious micas, several millimeters across. Several types of schist may be recognized, based on minerals which may be present:
Limestone to Marble Sandstone to Quartzite
Marble - fizzes in acid because its dominant minerals is calcite (or dolomite). The parent rock is limestone (or dolostone).
Quartzite - interlocking grains of quartz. Scratches glass. The rock fractures through the grains (rather than between the grains as it does in sandstone). The parent rock is quartz sandstone.
Commonly many small crystals merge to form larger crystals, such as the clay in shale becoming micas in slate, phyllite, and schist.
Olivine, pyroxene, and plagioclase in an original basalt change to amphiboles and chlorite (both commonly green)
At the highest grade of metamorphism the amphiboles are replaced by pyroxenes and garnets, the foliation is lost and a granulite that has a granulitic texture is produced.