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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