METAMORPHIC ROCKS

METAMORPHIC ROCKS sample rocks -Mica,' granite/gneiss,' shale/slate/schist,' sandstone/quartzite,' lime.stone/marble * * * * * METAMORPHIC means CHANGE! Metamorphic Rocks are rocks that have been changed from an existing type of rock, whatever it is. Metamorphic Rocks can be formed from Igneous Rocks, they can be formed from Sedimentary Rocks, and they can be formed from other metamorphic rocks. The rock they are formed from is called the Parent Rock - What does it take to change a rock into Metamorphic Rock? It takes great HEAT and PRESSURE It also often takes chemical reactions - due to the heat and pressure It also takes TIME Metamorphic Rocks begin to form 12 to 16 Kilometers below the surface of the Earth. At temperatures of 100* to 200* C and up to 800* C Keep in mind that water boils at 100* C 1- It is the great HEAT that makes rocks soft enough for the minerals in them to change The mineral crystals in the rock might change shape, they might change size, they may separat into layers. 2- The tremendous PRESSURE they are under (remember 12 to 16 Km under the surface?) Squeezes the minerals together - and makes them DENSER 3- Chemical reactions may also occur - so major changes in the rock's composition may occur The amount of heat, pressure and chemical reaction varies, so the change that occurs varies: If there is only a slight change - you can still identify the original rock It there is a great change - it is difficult to tell the original rock FINE GRAINED ROCKS ARE MORE EASILY CHANGED THAN COARSE GRAINED The new rock has new structures and new textures. Often the minerals in it have a distinct crystalline form. Metamorphic Rocks normally have larger crystals than their Parent Rock remember, the Parent Rock is the rock it was formed ft'om This is because the crystals have time to grow because they have extra heat and extra time.There are 2 types of Metamorphism: CONTACT METAMORPHISM- is when rocks are heated by contact with magma or lava around them. Usually the metamorphic change is seen only along the edges of the igneous formations. REGIONAL METAMORPHISM- occurs when deeply buried rocks are changed by

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METAMORPHIC ROCKS

increases in heat and pressure. Slates, Marble, Gneiss & Schists are formed this way . There are 2 basic types of Metamorphic Rocks based on their TEXTURE TEXTURE is the difference in orientation or alignment and size of the crystals FOLIATED - when the mineral crystals are flat and arranged in parallel layers or bands and tend to break along these layers or bands. Foliated metamorphic rocks form when mineral crystals in original rock recrystallize or flatten under pressure OR minerals of different densities separate into different layers. This gives a series of alternating dark and light bands in the rock. SHOW EXAMPLES: Mica - shows the flat crystals very well Granite can change to Gneiss, Slate can change to Schist The second type of metamorphic rock is called: UN-FOLIATED or NON-FOLIATEDNON -FOLIATED - This type of metamorphic rock does NOT have bands of crystals and it does NOT break into layers. It's crystals are irregularly oriented and it will break into angular pieces. SHOW EXAMPLES: Marble and Quartzite are NON- FOLIATED Shale can change to Slate Sandstone can change to quartzite Limestone can change to marble Now take 1 minute do you know the difference between contact metamorphism and regional metamorphism: Do you know the 2 main things that are required to make metamorphic rock Do you know the difference between foliated alld non-foliated rock There are 5 basic textures found in metamorphic rocks - they are Gneissose - Coarsely foliated with coarse mineral grains (G - nice -Os) Schistose - Finely foliated forming thin parallel bands along which the rock splits easily (Schist Os) Slaty Very fine folated - producing almost rigidly parallel planes of easy splitting (Slatey) Granoblastic - Unfoliated or finely foliated (Gran - 0 - blast - ick) Hornfelsic - Unfoliated with mineral grains that are commonly microscopic, breaks sharply into angular pieces. (Horn - fell - sick)

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