Topic II (Continued) What are “Rocks” Igneous Rocks Sedimentary Rocks The Rock Cycle Igneous Rocks Sedimentary Rocks Metamorphic Rocks

Rocks are mixtures of minerals..

There are 3 major classes of rock. Igneous rocks form when hot molten rock material cools and hardens.

Sedimentary Rocks Sedimentary rocks form when bits and pieces of other rocks are weathered and eroded away, accumulate (usually in a large body of water), and are cemented together.

Metamorphic rocks….. form when other rocks are altered by heat, pressure, and/or chemical action.

The rock cycle “begins” with each of the 3 major rock groups…. Igneous Metamorphic Sedimentary

Igneous rock can weather and erode to from sediments... Metamorphic Sedimentary

Which can be cemented together to form Sedimentary rocks Igneous Sediments Metamorphic Sedimentary

These rocks can then melt to form magma... Igneous Sediments Metamorphic Magma Sedimentary

Which cools and hardens to form Igneous rock Sediments Metamorphic Magma Sedimentary

The igneous rock could also be heated &/or pressurized…. Sediments Metamorphic Magma Sedimentary

to form a new Metamorphic rock. Igneous Sediments Metamorphic Magma Sedimentary

Or the Igneous rock could melt and cool to form a new Igneous rock. Sediments Metamorphic Magma Sedimentary

The Metamorphic rock could also melt and cool to form a new Igneous rock. Sediments Metamorphic Magma Sedimentary

The Metamorphic rock could also erode to form sediments…. Igneous Sediments Metamorphic Magma Sediments Sedimentary

which is cemented together to form a new sedimentary rock. Igneous Sediments Metamorphic Magma Sediments Sedimentary

The sedimentary rock can be heated &/or pressurized to form a metamorphic rock. Igneous Sediments Metamorphic Magma Sediments Sedimentary

The sedimentary rock can be eroded to form sediments….... Igneous Sediments Metamorphic Magma Sediments Sedimentary

Which are cemented together to form new sedimentary rocks. Igneous Sediments Metamorphic Magma Sediments Sedimentary

Finally, the metamorphic rock can be heated and pressurized…. Igneous Sediments Metamorphic Magma Sediments Sedimentary

to form a new metamorphic rock. Igneous Sediments Metamorphic Magma Sediments Sedimentary

The Rock Cycle

Igneous Rocks Igneous rocks form when hot liquid rock called magma (if it is deep within the earth) or lava (if it is near or at the earth’s surface) cools and hardens.

Igneous rocks are classified as being “Intrusive” of “Extrusive” Extrusive igneous rocks (aka “Volcanics”) form as lava cools and hardens at or near the earth’s surface.

“Fogol” erupts, throwing extrusive rocks into the air……

“Intrusive” (aka “Plutonic”) These rocks form deep in the earth as magma cools and hardens.

Crystal size and cooling time... As minerals take form, molecules “fall into place” layer upon layer in a definite orderly pattern. Minerals which cool over a long period of time will therefore develop large crystals.

Rapid cooling, however…. does not permit the atoms to arrange themselves in an orderly pattern. Thus, rocks which cool quickly usually have a glassy or fine texture.

Igneous rocks can be identified by their….. Color - Is the mineral dark or light ? This color usually reflects the mineral composition of the rock Texture - Is the rock coarse grained (crystals are easily visible with the naked eye), fine grained (crystals are only visible with a magnifier) or glassy (no crystals are visible even under magnification) ?

Use your Earth Science Reference Tables to identify igneous rocks….

If your sample is light colored..

and is fine grained…..

The rock must be Rhyolite