Earth Materials Metamorphic rocks Web addressed for pictures are in the notes section.

I. Metamorphic Rocks are ‘changed’ rocks 1. They can form from any other rock or rock type.

2. These form 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).

3. Metamorphic rocks are recrystallized/ altered versions of pre-existing rock. The minerals often just line up differently, but intense metamorphism will cause new minerals to form.

II. Metamorphic Rocks are formed from: a. Heat: contact metamorphism When magma ‘bakes’ a nearby rock. (at volcanoes, mid- ocean ridges, igneous intrusions)

b. Chemical changes: At mid-ocean ridges when seawater and sediments mix with hot gases

c. Pressure: Regional Metamorphism Occurs in 3 environments: At subducting boundaries when rock is ground and deformed

When mountains form by tension, compression

Overlying sediments exert so much pressure they change the deep rock

III. The two main groups of metamorphic rocks are the Foliated and Non-foliated

1. The foliated rocks: a. Texture: foliation or banding are present. The minerals ‘line up’. This is seen by observing the texture of the rock

b. caused by intense pressure from regional metamorphism minerals align at a perpendicular to the direction of the pressure. This often forms the foliated texture.

c. Types of foliation in ESRT Banding: ribbons of different minerals Mica in the rock indicates regional metamorphism

2. Nonfoliated rocks: a. the composition of the rock is important. Ex. Quartzite and marble Try and identify the minerals (the acid test identifies marble and hardness shows which is quartzite).

b. Formed often as contact metamorphic rocks: Rocks changed by intense heat. They are recrystallized due to the presence of nearby lava or magma flows, which partially melt the rock.

c. are found along igneous intrusions where the magma heats the rock. They PROBABLY do not show foliation.

Identifying metamorphic rocks is pretty tricky, and requires patience (and sometimes a good stereomicroscope)