GEOLOGY MACC Bill Palmer Lecture 4 Rocks

What are Rocks? Rocks are solid materials that comprise nearly all of the earth (and moon and planets). Rocks are almost always aggregates of minerals. (This is why we study minerals first).

What is the Rock Cycle?  The rock cycle explains how all rocks can be formed, deformed transformed, destroyed, and reformed as a result of natural processes.

Rock Cycle Materials for forming rocks comes from: 1) the Earth’s mantle (molten rock is magma when in the ground and lava when it erupts on the surface) 2) Space (meteorites) 3) Organisms (plants and animals) 4) Fragmentation and decay of other rocks and minerals

Rock Cycle There are three main rock groups: 1) IGNEOUS ROCKS –Form when magma or lava cool. 2) SEDIMENTARY ROCKS- Form when chemical residues and fragments of plants, animals, crystals, or rocks, or sand are compressed and cemented together. Also form from chemical precipitation. 3) METAMORPHIC ROCKS- Form when other rocks are changed by heat, pressure, or hot fluids.

The Rock Cycle

Rock Properties  1. General form-smooth, rough, irregular  2. Color-light, dark,  3. Grains-sand, gravel, crystals, fossils, fragments  4. Shape-teardrop, icicle, smooth, sphere

Rock Properties  5. Texture is very important-  Glassy  Fine-grained, <1mm  Coarse-grained, >1mm  Vesicular-bubbles  Foliated-layers  Clastic-”clasts” of plants, animals, minerals

Igneous Rocks  Intrusive Igneous Rocks-Magma is the source and the rocks cool slowly beneath the ground and form large crystals.  Extrusive Igneous Rocks-Lava is the source and the rocks cool quickly above the ground and form small crystals.

INTRUSIVE STRUCTURES 1. Batholith-Massive, no “bottom” 2. Sills-Sheet-like between layers of other rocks 3. Laccolith- “Blister-like” 4. Pipe-vertical tube 5. Dikes-Layers vertical to rock 1. Radial 2. Sheet 3. Ring

EXTRUSIVE  Lava Flows  Pyroclastic deposits (fire fragments)

How to Analyze Igneous Rocks  STEP 1 and 2-Study the Color and Mineral Composition  Light- Felsic Minerals (feldspar)  Quartz (gray, white)  Plagioclase Feldspar (white)  Potassium Feldspar (pink)  Muscovite Mica (clear, brownish)

How to Analyze Igneous Rocks  STEP 1 and 2-Study the Color and Mineral Composition  Dark-Mafic Minerals (no feldspar)  Biotite Mica (black)  Amphibole (dark gray)  Pyroxene (dark green)  Olivine (green)

How to Analyze Igneous Rocks  STEP 3-Study the Texture  Intrusive  Pegmatitic (crystals >1 cm)  Phaneritic (crystals 1-10 mm)  Porphyritic (large and small crystals indicate that it cooled at TWO different rates)

How to Analyze Igneous Rocks  STEP 3-Study the Texture  Extrusive  Porphyritic (large and small crystals indicate that it cooled at TWO different rates)  Aphanitic (crystals < 1mm)  Glassy (like glass, crystals too small to see)  Vesicular (small or large bubbles, like pie meringue or froth)  Pyroclastic- particles emitted from volcano

Now, put it all together!

What is this Igneous Rock?  Light or Dark?  Coarse or Fine Grained?  What is it?

What is this Igneous Rock?  Granite

What is this Igneous Rock?  Light or Dark?  Coarse or Fine Grained?

What is this Igneous Rock?  Granite  Yes, both are granite-one gray and one red!

What is this Igneous Rock?  Light or Dark?  Coarse or Fine Grained?

What is this Igneous Rock?  Gabbro

What is this Igneous Rock?  Light or Dark?  Coarse or Fine Grained?

What is this Igneous Rock?  Rhyolite

What is this Igneous Rock?  Light or Dark?  Coarse or Fine Grained?  Be careful with this one, it is really very fine grained with some larger white minerals.

What is this Igneous Rock?  Rhyolite Porphyry

What is this Igneous Rock?  Light or Dark?  Coarse or Fine Grained?  What is the unique texture?

What is this Igneous Rock?  Pumice

What is this Igneous Rock?  Light or Dark?  Coarse or Fine-grained?  What is the unique texture?

What is this Igneous Rock?  Scoria

What is this Igneous Rock?  Light or Dark?  Coarse or Fine grained?

What is this Igneous Rock?  Basalt

Some Igneous Rocks to Know  Granite  Gabbro  Rhyolite  Basalt  Scoria  Pumice  Rhyolite Porphyry

Wrap-ups 1. What are rocks? 2. What is the Rock Cycle? 3. What is the difference between magma and lava? 4. What are the three types of rocks? 5. What is a batholith? Sill? Laccolith?

Wrap-ups Name the rock described: 6. Light colored, coarse grained. 7. Dark colored, coarse grained. 8. Light colored, very fine grained 9. Spongy looking and light in color. 10. Dark and glassy looking.