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Earth Materials. Topic 3. Metamorphic rocks Web addressed for pictures are in the notes section. They can form from any other rock or rock type. Metamorphic Rocks are ‘changed’ rocks. a. Heat: contact metamorphism
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Earth Materials Topic 3. Metamorphic rocks Web addressed for pictures are in the notes section.
They can form from any other rock or rock type. Metamorphic Rocks are ‘changed’ rocks
a. Heat: contact metamorphism When magma ‘bakes’ a nearby rock. (at volcanoes, mid-ocean ridges, igneous intrusions) Metamorphic Rocks are formed from:
b. Chemical changes:At mid-ocean ridges when seawater and sediments mix with hot gases
Occurs in 3 environments: At subducting boundaries when rock is ground and deformed c. Pressure: Regional Metamorphism
when pre-existing rocks are changed due to heat and pressure. (If the old rock melts, then it does not become metamorphic, because melted rock produces magma and igneous rock). 1. Metamorphic rocks form:
The minerals often just line up differently, but intense metamorphism will cause new minerals to form. 2. Metamorphic rocks are recrystallized/ altered versions of pre-existing rock.
3. Metamorphic rock are classified according to: • The presence or type of foliation, which is seen by observing the texture of the rock.
b. The second identifier is the mineral composition when discussing the nonfoliated rocks. For example, marble and quartzite look a lot alike, but are made of very different minerals.
Ex. Quartzite and marble (the acid test identifies marble and hardness shows which is quartzite). Nonfoliated rocks: composition
The foliated rocks: a. Texture: foliation or banding
minerals align to the direction of the pressure. This often forms the foliated texture. 4. Rocks formed by intense pressure from regional metamorphism;
Because they are usually bands of rock that are recrystallized due to the presence of nearby lava or magma flows, which partially melt the rock. 5. Rocks formed by intense heat are contact metamorphic rocks:
do not show foliation. 7 Contact metamorphic rock are found along igneous intrusions where the magma heats the rock.
Contact metamorphic rocks • Zones of metamorphic rocks usually are found between igneous rocks and other rocks.
Banding: ribbons of different minerals Mica in the rock indicates regional metamorphism Types of foliation in ESRT