Organizing Metamorphic Rocks Metamorphism: the process that creates metamorphic rocks. All made from the alteration of existing rocks by excessive… pRESSURE AND/OR hEAT The most obvious effect is the rearrangement of minerals grains into bands or stripes called foliations. Temperatures above 200oC will create new minerals in the rock or will enlarge existing minerals known as recrystallization Two types of MR: sorted by texture - no particular direction 1. Foliated – bands or stripes 2. Non-Foliated The mineral grains in rocks subjected to extreme pressure often rearrange themselves in a parallel fashion. Examples: Foliated – Non-Foliated –

How does metamorphism happen? What force has the power to squish & heat rocks until the crystals change? Regional Metamorphism Occurs over large areas (as big as states or countries!) Existing rock will change by the heat and pressure created during mountain building. (A) continents collide (B) ocean crust subducts

How does metamorphism happen? What force has the power to squish & heat rocks until the crystals change? Contact metamorphism Occurs over small areas. Existing rock is heated when it comes in contact with magma or lava.

This sill baked the adjoining limestone into marble. The lava flow (in gray) seen in this road cut has baked the mud beneath it into brick.

Metamorphic Rocks Come From “Other Rocks” Rock Type Parent Rock Metamorphic Rock SR Shale Slate MR Slate Phyllite MR Phyllite Schist MR Schist Gneiss SR Sandstone Quartzite SR Limestone Marble IR Basalt Schist IR Granite Gneiss