Metamorphic and Igneous Rock Definitions

Foliated In metamorphic rocks where the rocks have minerals arranged in parallel bands

Unfolitated In metamorphic rock where the crystals are NOT arranged in bands

Dynamic or Regional metamorphism Metamorphic rock that is formed over a large area where the rocks are buried deep in the earth and are changed by temperature and pressure

Thermal or Contact Metamorphism Type of metamorphism that occurs when rocks are heated by contact with magma or lava

Chemical Reaction A process that changes the object from one thing into something new

Igneous Rock Rock formed by heating and cooling of magma or lava

Felsic Light or less dense, a lot of silica (very explosive magma) Ex. Granite pumice

Mafic Dark, more dense and little silica (shield volcanoe lava like the ones in Hawaii) Ex. gabbro

Intrusive Igneous rock formed DEEP within the earth, cools very slowly

Extrusive Igneous rock formed on the surface of the earth, cools quickly

Porphyritic An igneous rock whose cooling rate has changed and there are two more different size crystals in the rock Ex. porphyry

Glassy The texture of an igneous rock that cools so quickly no crystals can form Ex. obsidian

Fine-grained The texture of an igneous rock that has small crystals because it cooled quickly Ex. basalt

Coarse-grained The texture of an igneous rock that has cooled slowly and has LARGE crystals. Ex. granite

Plutons LARGE intrusive rock formations, they may produce landforms by pushing up the land above

Lava Plateau Layers of lava that build up on a flat area of the earth’s surface

Dike Narrow, flat formation of igneous rock formed in vertical cracks in the existing rocks

Laccolith Domelike intrusion that pushes overlying rocks into an arch and has flat floor

Metamorphic rock A metamorphic, sedimentary or igneous rock that undergoes change due to tremendous heat, great pressure or chemical reactions

Sill Sheet like mass of rock that squeezes in between other layers of rocks

Batholith HUGE, irregularly shaped intrusion that extends deep into the earth’s crust

Stock Intrusion that is similar to a batholith that has an exposed area of less than 100 square kilometers

Volcano Place where magma reaches the earth’s surface