EQ: How are rocks formed? ls streak the EQ: How are rocks formed? Standard S6E5.c Classify rocks by their process of formation.
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 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 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 Shape a. smooth and rounded (conglomerate) b. jagged (breccia) Grain Pattern a. foliated (gneiss) -lie in flat layers . vy, -wavy, swirling patterns b. nonfoliated (marble) c. looks like rows of multicolored beads d. occur randomly No Visible Grain a. have no apparent grains
Mineral 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 Origin Origin - 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 rock b. organic rock c. chemical rock 3. metamorphic rock = formed when existing rock is changed by heat, pressure, or chemical reactions a. foliated rock b. nonfoliated rock
Compare 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