Post on 04-Jan-2016
Chapter Three
ROCKS
Section 3-1 Classifying Rocks
• When studying a rock sample, geologists observe the rock’s color and texture and determine its mineral composition.– Using color and texture, geologists can classify
a rock according to its origin.– Texture is the look that results from the size,
shape, and pattern of the rocks grains.
3-1
• Coarse-grained: the grains are large and easy to see.
• Fined-grained: the grains are small and can been seen under a microscope or hand-lens.– Some rock’s grains results from the shape of
the crystals that form the rock.– In other rocks, the grain shapes result from
fragments of other rock.
Texture
Texture
3-1
• The three major groups of rock are:– Igneous: forms from the cooling of molten
rock.– Sedimentary: forms when particles of other
rocks of the remains of plants and animals are pressed and cemented together.
– Metamorphic: forms when an existing rock is changed by heat, pressure, or chemical reactions.
3-2 Igneous Rock
• Igneous rock is any rock that forms from magma or lava. Most igneous rocks are made of mineral crystals. Igneous rocks are classified according to their origin, texture, and mineral composition.
Extrusive Rock
– Extrusive rock: is igneous rock formed from lava that erupted onto Earth’s surface.
• Basalt is the most common extrusive rock.
Samples of Extrusive Rock
3-2
– Intrusive rock: Igneous rock that formed when magma hardened beneath the Earth’s surface.• Granite is the most abundant intrusive
rock.– The texture of an igneous rock depends
on the size and shape of its mineral crystals.
• Texture may be fine-grained, coarse-grained, porphyritic, or glassy.
– Fined-grained: rapid cooling lava forms fined-grained.
– Coarse-grained: slow cooling lava forms coarse-grained.
– Porphyritic: large crystals scattered on top of small crystals. This occurs when magma cools in two stages, first slow, and then rapidly as magma moves near to the surface.
Samples of Intrusive RockGranite
Samples of Intrusive RockGabbros
Samples of Intrusive RockDiorite
3-2
• Lava low in silica forms dark-colored rocks, such as basalt.
• Magma that is high in silica usually forms light colored rocks, such as granite.
• Many igneous rocks are hard, dense, and durable. People use igneous rock for tools and building materials.
3-3 – Sedimentary Rock
• Sedimentary rocks form from particles deposited by water and wind. Sand, mud, and pebbles. Sediment is small, solid pieces of material that come from rocks or living things.
1. Erosion: running water or wind loosen and carry fragments of rock.
2. Deposition: the process by which sediment settles out of the water or wind.
3. Compaction: the process that presses sediments together.
4. Cementation: the process in which dissolved minerals crystallize and glue particles of sediment together.
3-3
• There are three major groups of sedimentary rocks:
– Clastic rock: sedimentary rock that forms when rock fragments are squeezed together. Sandstone is a clastic rock formed from the compaction and cementation of sand.
– Organic Rock: forms where the remains of plants and animals are deposited in thick layers. Coal is formed from the remains of swamp plants and limestone is formed from the hard shells of living things – seashells.
– Chemical Rock: when minerals that are dissolved in a solution crystallize. Chemical rocks also form from mineral deposits left when seas or lakes evaporate.
Samples of Sedimentary Rock
• Sandstone
Samples of Sedimentary Rock
• Gypsum
Samples of Sedimentary Rock
• Shale
3-4 Rocks from Reefs
• Coral animals are tiny relatives of jellyfish that live together in vast numbers. They build skeletons that grow together to form a structure called a coral reef.
• Coral reefs only form in warm, shallow tropical waters.
• When coral animals die, their skeletons remain, and new corals build on top of them.
• There are three types of coral reefs: fringing reefs, barrier reefs, and atolls.
• A coral reef is really organic limestone.
Barrier Reef
Coral Reefs
Coral Reefs
3-5 Metamorphic Rock
• Every metamorphic rock is a rock that has changed its form. Heat and pressure deep beneath Earth’s surface can change any rock into metamorphic rock. Metamorphic rock can form out of igneous, sedimentary, or other metamorphic rock.– Geologists classify metamorphic rocks by the
arrangement of the grains that make up the rocks.• Metamorphic rocks that have their grains arranged in parallel
layers or bands are said to be foliated – slate is the most common.
• Metamorphic rocks that have grains arranged randomly. Marble and Quartz.
Metamorphic Rock Samples
Metamorphic Rock Samples
• Marble
Metamorphic Rock Sample
• Quartz
3-6 Rock Cycle
• Forces inside Earth and at the surface produce a rock cycle that builds, destroys, and changes the rocks in the crust.– The rock cycle is a series of processes on and
beneath Earth’s surface that slowly change rocks from one kind to another.
Rock Pictures - Lava
• http://www.hoho.co.uk/html/lanzarote_lava_and_rocks.html