EQ: How are rocks formed?

EQ: How are rocks formed?

Standard S6E5.c

Classify rocks by their process of formation.

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EQ: How Are Rocks Classified?EQ: How Are Rocks Classified?

• What three characteristics do scientists use to identify rocks?

• What are the three groups into which geologists classify rocks?

• What is a rock’s texture?

• What do the three major groups of rock have in common? How are they different?

How geologists Classify RocksHow geologists Classify Rocks

• Rocks are made of minerals and a mixture of other materials

• Some rocks are made of a single mineral

• When studying a rock sample, geologists observe the rock’s texture, origin and mineral composition

A Rock’s TextureA Rock’s Texture

• A rock’s texture is the size, shape, and pattern of the rock’s grains

Grain Size a. fine-grained (small-basalt)b. coarse-grained (large-granite)

Grain Shapea. smooth and rounded (conglomerate)b. jagged (breccia)

Grain Patterna. foliated (gneiss)

-lie in flat layers . vy, -wavy, swirling patterns

b. nonfoliated (marble)c. looks like rows of multicolored beadsd. occur randomly

No Visible Graina. have no apparent grains

Mineral CompositionMineral Composition

• By looking at a small sliver of a rock under a microscope, geologists can observe the size and shape of the crystals and identify the minerals the rock contains

• Also, geologists can do tests to identify the physical properties of the minerals inside the rock.

• mafic= dark-colored rocks (poor in silica) (basalt)• felsic = light-colored rocks (rich in silica) (granite)

Rock OriginRock OriginOrigin - how and where the rock was formed

1. igneous rock = forms from the melting, cooling and hardening of molten rock

a. extrusive= formed above the surface (lava)b. intrusive = formed below the surface (magma)

2. sedimentary rock = forms in layers from other rocks, plants, and animals through a process of

weathering, erosion, deposition, compaction and cementation

a. clastic rockb. organic rockc. chemical rock

3. metamorphic rock = formed when existing rock is changed by heat, pressure, or chemical reactions

a. foliated rockb. nonfoliated rock

Compare and Contrast RocksCompare and Contrast Rocks

Compare – Rocks in each group make up the Earth’s crust and are composed of minerals and other materials

Contrast – Rocks are different in the way they are formed