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ROCK NOTES
Rocks – a solid made up of a mixture of minerals, glass and organic material.
Three Categories of Rocks
1. Igneous
2. Sedimentary
3. Metamorphic
Igneous Rocks
Igneous Rocks – formed from magma which has cooled and hardened.
Three ways to classify igneous rocks
1. Where did they form ….intrusive/extrusive *
2. Texture … …………….crystal size, grain patterns
3. Mineral composition … what minerals make-up
the rock
Intrusive – inside the Earth. cools slowly, forms large crystals and large grain patterns
Ex. Granite
Extrusive – outside the Earth. cools quickly, forms small or no crystals. Fine grain pattern
Ex. Obsidian
Porphyry – Magma cools slowly at first thenquickly. Large crystals are formed
which are embedded within a mass of smaller crystals.
ex. D.Q. Blizzard
Mineral Composition – rocks are categorized by the minerals that they contain
or by the amount of minerals they contain.
Family
Mineral
Coloring
Examples
Felsic
high silica content
light color
Granite/Rhyolite
Mafic
low silica content
dark color
Gabbro/Basalt
Intermediate
no quart
combination of colors
Diorite/Andesite
Rock that contain the same mineral may not be the same type of rock based on where they cool.
A rock with high silica content that cools intrusively is granite.
A rock with high silica content that cools extrusively is rhyolite
Rocks that come from the same type of magma but cool differently create different rocks
Intrusive
Extrusive
Granite ……………………….Rhyolite
Gabbro ……………………….Basalt
Diorite ……………………….Andesite
Obsidian
Pumice
Scoria
Sedimentary Rock Notes
Sedimentary rock – a combination of particles from other rocks, glass and organic matter which are
compacted or cemented together to form a new rock.
Three types of sedimentary rocks
1. Clastic Rocks
2. Chemical Rocks
3. Organic Rocks
Clastic Rocks - Formed from particles of other rocks which have accumulated and hardened.
A mixture of other rocks.
Weathering – process of breaking down larger rocks by wind, water and ice. These particles
are transported to other locations where they join fragments from other rocks.
These particles join together and hardened to form new sedimentary rocks.
3 types of clastic rocks – Based on particle size.
1. Pebble to boulder size
Conglomerates – clastic rocks composed of rounded rock particles.
Breccia – clastic rocks composed of angular, sharp cornered fragments
2. Sand size grains - Sandstone
3. Clay sized particles - Shale
Chemical rocks – Sedimentary rock which form from minerals which were once dissolved in water.
Evaporite – When water evaporates and the minerals which were left behind form a solid rock
Gypsum and halite are examples of chemical rocks Great Salt lake, Utah.
Organic Rocks – Sedimentary rock which are formed from the remains of living things.
Coal – decayed plants buried and compacted into matter which is mostly carbon.
Limestone – formed from the shells of sea organisms such as clam and oysters
Chalk – a type of limestone. White cliffs of Dover.
Sedimentary Rock Features - help identify sedimentary rocks.
Stratification – layering resulting from changes in the type of sediment being deposited.
Ripples marks – wavy marks caused by the action of wind or water on sand.
Mud Cracks – Formed when muddy deposits dry & shrink.
Fossils – remains or traces of ancient plants or animals.
Geode – crystal filled cavities in sedimentary rocks.
Metamorphic Rocks
Metamorphic Rocks – rocks formed from other rocks as a result of intense heat, pressure (recycling).
Two types of metamorphism
1. Contact metamorphism - when existing rock comes into contact with hot magma.
2. Regional metamorphism – when large areas of existing rock is changed due to heat and pressure
which occurs during plate tectonics. Most metamorphic rock is formed
as a result of regional metamorphism
Classification of metamorphic rock
Foliated – rocks with visible layers or bands
Unfoliated – rock which do not have layers or bands.
Examples
Metamorphic Rocks
Sandstone ..………….HEAT & PRESSURE……….... Quartzite
Granite ………………………………………………... Gneiss
Limestone …………………………………………….. Marble
Shale ……………………………………………..…... Slate
Rock Cycle
Rock Cycle - a process by which rocks are changed from one form to another.
Igneous rock …………………………….. melting and cooling
Sedimentary rock ……………………….. weathering and erosion
Metamorphic rock ………………………… heat and pressure
Rock Cycle