Igneous rocks Crystallize from a molten rock: magma Magma: liquid rock beneath earth’s surface Lava: liquid rock above earth’s surface Igneous rocks classified on Mineral size composition

Igneous rocks Intrusive igneous rocks Extrusive igneous rocks Cool below ground (slowly) All minerals visible w/out microscope Extrusive igneous rocks Cool above ground (fast) Most minerals too small to see w/out microscope

Igneous rocks Intrusive igneous rocks Extrusive igneous rocks

Intrusive or extrusive?

Slow or fast cooling?

Intrusive or extrusive?

Slow or fast cooling?

Light colored igneous rocks Granite and rhyolite

Intermediate igneous rocks Andesite

Dark colored igneous rocks Gabbro and basalt

Aphanitic Texture – Rapid Cooling Small Crystals

Phaneritic Texture – Slow Cooling Large Crystals

Glassy Texture - Very Rapid Cooling - No Crystal Structure

Where do igneous rocks form?

What is left behind when igneous rocks cool?

Rock Cycle Igneous rocks can become what other kind of rocks?

Metamorphic rocks Formed by transformation of other rocks Heat and pressure do this transforming! End up with New minerals And/or texture changes

Metamorphic textures Foliated: alignment of minerals Rock looks banded/layered Nonfoliated: random orientation of minerals

Foliated or nonfoliated?

Foliated metamorphic rocks Smallest minerals Slate Clue: like shale/mudstone but harder

Foliated metamorphic rocks Schist Shiny with bigger minerals

Foliated metamorphic rocks Gneiss Big minerals Looks like a granite with bands of color

Nonfoliated met. rocks Marble Made of calcite Best way to ID?

Nonfoliated met. rocks Quartzite Can look like marble, but no fizz with acid Hand out met rocks to ID

Nonfoliated met. rocks Greenstone Clue: green basalt

Rock Cycle

Sedimentary rocks Clastic sed rock: made of solid particles once part of other rocks Classified by grain size Chemical sed rock: made from dissolved material in water Classified by chemical composition Biochemical sed rock: made of dead plants and animals

Biochemical, chemical, or detrital?

Clastic sed rocks Big particles Conglomerate Sand size Sandstone Small particles Mudstone (shale)

Clastic sed rocks Conglomerate Clue: Particles of lots of different sizes

Clastic sed rocks Sandstone Clue: feels sandy

Clastic sed rocks Mudstone (shale) Clue: very small particles No grit when you taste it

Chemical sed rocks Limestone Made of calcite Clues: fizzes with acid Often contains fossils

Chemical sed rocks Rock salt/halite Gypsum Clue: tastes salty Clue: easily scratched, not salty

Biochemical sed rocks Category of chemical sed rocks Coal Limestone if with fossils

Importance of sed rocks Key to interpreting Earth’s history

Homework Go to website and complete the relative age assignment. Other website for checking to see if you are on the right track! Websites are on our class page