| Rock notes continued... METAMORPHIC ROCKS - "CHANGE" 1. Metamorphic rock forms when rock (Igneous or Sedimentary) is changed by HEAT or PRESSURE or BOTH - HEAT AND PRESSURE. 2. Rocks beneath the earth's surface are under great pressure from overlying rock layers. 3. They are also exposed to heat from magma deep in the earth. 4. IF the HEAT and PRESSURE are NOT great enough to MELT the rocks, the MINERAL grains in the rock MAY CHANGE IN SIZE OR SHAPE. 5. IF the HEAT and PRESSURE are great enough, the rock may MELT and MAGMA forms. 6. Some minerals are FLATTENED, and some COMBINE with surrounding minerals to form NEW or BIGGER minerals. 7. Metamorphic change can form TWO types of Metamorphic rocks: A. FOLIATED TEXTURE - form when the minerals in the original rock FLATTEN under PRESSURE. The mineral grains flatten and line up in VISIBLE PARALLEL BANDS. 1. Examples of foliated rocks are Slate and Gneiss. 2. Slate forms from Sedimentary rock. Shale under Heat and Pressure. Slate can be easily separated along its foliation layers. 3. Gneiss forms when a GREAT DEAL OF PRESSURE is applied to the Igneous rock Granite. The minerals in Granite are rearranged into alternating bands. B. NONFOLIATED TEXTURE - The mineral grains CHANGE, COMBINE, AND REARRANGE, but they DON'T form VISIBLE BANDS. They don't separate easily into laers, they Fracture into pieces of random size and shape. 1. Marble is an example of Nonfoliated Metamorphic Rock. 2. Marble forms from the Sedimentary Rock Limeston. |
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