Rocks. Definition of Rock. A rock is a hard material made of one or more minerals A rock can be made of only one mineral entirely ( monomineralic ) or a mixture of many minerals ( polymineralic ). Where are rocks found?. Rocks are found in Earth’s mantle and crust
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Definition of Rock A rock is a hard material made of one or more minerals A rock can be made of only one mineral entirely (monomineralic) or a mixture of many minerals (polymineralic)
Where are rocks found? • Rocks are found in Earth’s mantle and crust • This is because the inner core and outer core are too hot. The iron and nickel in these layers cannot solidify into rocks • Rocks from different distances
3 groups of rocks • A rock is a group of minerals joined together in some way • Igneous – formed by the cooling & solidification of molten rock (magma) • Sedimentary – formed by the compaction & cementation of layers of sediment (rock fragments, organic remains, chemical deposits) • Metamorphic – formed when existing rocks are CHANGED by intense heat & pressure but DO NOT MELT
The ROCK CYCLE shows how each type of rock forms & how each rock can change into a different type of rock • Rocks gradually and continually change from one type to another
Igneous Rocks ESRT page 6
Igneous rocks form from the cooling or SOLIDIFICATION of magma (melted rock) The RECRYSTALLIZATION of minerals is evident in Igneous Rocks
LIQUID HOT MAGMA • Magma is a mixture of liquid rock, crystals, and gas • Magmas are less dense than surrounding rocks, and will therefore move upward
The cooling rate of magma takes differs, causing the crystal size to also differ
intrusive igneous rocks • Form by the cooling of magma UNDERGROUND • “IN” –trusive / “IN” the ground Also known as PLUTONIC
Underground cooling is SLOWER • Rock crystals are LARGE & have a coarse texture
gabbro pegmatite granite
extrusive igneous rocks • Forms from the cooling of LAVA (magma that has reached earth’s surface)
Cools QUICKLY (exposed to colder air) • Rock crystals are SMALL and rocks have a fine/glassy texture
Rate of Cooling Activity • When I say “Go” try to find other students in the class who have the same color that you have- PLEASE WALK! • When I say “Stop”, stop exactly where you are and do not move until I say “GO” again • What happened as I gave you a longer amount of time to find each other?
Pumice is an Extrusive Igneous Rock that is VESICULAR (has gas pockets). Because pumice formed so quickly, the rock formed around the pockets of gas, creating “holes” in the rock. This allows the rock to float in water because of its lower density
All light in color, low in density, made up of the same minerals, and felsic in composition…. What’s the difference? COOLING TIME!
Key idea: -The texture of the igneous rock is determined by the size, shape, and arrangement of the mineral crystals NOT if it is smooth or bumpy -Rock texture is by SIGHT/SIZE, not by TOUCH
FELSIC MAGMA Light colored Thick (high viscosity) Contains high amounts of silica Granite MAFIC MAGMA Dark colored Thin (low viscosity) Contains high amount of magnesium & iron Basalt types of magma
the “bells & whistles” for identifying an IGNEOUS rock Igneous rocks have obvious CRYSTALS If you see minerals, it’s probably igneous!