| Word |
Definition |
| aureole |
A zone or halo of contact metamorphism found in the host rock surrounding an igneous intrusion. |
| burial metamorphism |
Low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata. |
| compressional stress |
An inward pressure or stress that squeezes the rock, reducing its volume. |
| confining pressure |
An environment where forces are applied equally in all directions. |
| contact metamorphism |
Changes in rock caused by the heat of a nearby magma body. |
| differential stress |
An environment where forces are not applied equally in all directions. |
| foliation |
A term for a linear arrangement of textural features often exhibited by metamorphic rocks. |
| gneiss |
Medium-to-coarse-grained banded metamorphic rocks in which granulated and elongated minerals dominate. |
| gneissic texture |
A metamorphic texture in which dark and light silicate minerals have separated, giving the rock a banded appearance. |
| hornfels |
A fine-grained nonfoliated metamorphic rock formed from various minerals. |
| hydrothermal metamorphism |
Chemical alterations that occur as hot, ion-rich water circulates through fractures in rock. |
| impact metamorphism |
Metamorphism that occurs when meteorites strike Earth's surface. |
| index mineral |
A mineral that is a good indicator of the metamorphic environment in which it formed. Used to distinguish different zones of regional metamorphism. |
| marble |
A relatively soft, nonfoliated metamorphic rock formed from limestone or dolostone. |
| metamorphic grade |
The degree to which a parent rock changes during metamorphism. It varies from low grade (low temperatures and pressures) to high grade (high temperatures and pressures). |
| metamorphism |
The changes in mineral composition and texture of a rock subjected to high temperature and pressure within Earth. |
| metasomatism |
A significant change in the chemical composition of a rock, usually by the addition or removal of ions in solution. |
| migmatite |
A rock exhibiting both igneous and metamorphic rock characteristics. Such rocks may form when light-colored silicate minerals melt and then crystallize, while the dark silicate minerals remain solid. |
| nonfoliated texture |
Texture associated with metamorphic rocks that do not exhibit foliation. |
| parent rock |
The rock from which a metamorphic rock is formed. |
| phyllite |
A metamorphic rock composed mainly of fine crystals of muscovite, chlorite or both. |
| porphyroblastic texture |
A texture of metamorphic rocks in which particularly large grains are surrounded by a fine-grained matrix of other minerals. |
| quartzite |
A hard, nonfoliated metamorphic rock formed from quartz sandstone. |
| recrystallization |
The formation of new mineral crystals in a rock that tend to be larger than the original crystals. |
| regional metamorphism |
Metamorphism associated with large-scale mountain building. |
| schist |
Medium-to-coarse-grained metamorphic rocks having a foliated texture, in which platy minerals dominate. |
| schistosity |
A type of foliation characteristic of coarser-grained metamorphic rocks. Such rocks have a parallel arrangement of platy minerals such as the micas. |
| slate |
A very-fine-grained metamorphic rock containing platy minerals and having excellent rock cleavage. |
| slaty cleavage |
The type of foliation in which there is a parallel arrangement of fine-grained metamorphic minerals. |
| texture |
The size, shape, and distribution of the particles that collectively constitute a rock. |
