what is a rock? a rock is a mixture of minerals and other materials
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FORMATION OF ROCKS
Rocks are categorized by how they were formed.
Igneous: about 150 rocks
Sedimentary –about 50 rocks
Metamorphic – about 300 rocks
CLASSIFYING ROCKS
Using these properties, Geologists can classify a rock according to its origin – or how the rock formed.
Color TextureMineral
Composition
Geologists classify rocks into 3 major groups: Igneous rock: from cooled magma/lavaSedimentary rock: from weathered sediment compressed
Metamorphic rock: existing rock changed from heat/pressure (forms underground)
When studying a rock sample, geologists observe the rock’s:Mineral composition: can be 1 or many more that make up a rock
Color: lightness/darknessTexture: Grain size, grain shape, grain pattern
IN SUMMARY…
They are either intrusive (formed beneath surface) or extrusive (formed above Earth’s surface)
CLASSIFYING IGNEOUS ROCKSBY ORIGIN
Basalt rock
CLASSIFYING IGNEOUS ROCKSBY TEXTURE
Fine grained Course-grained
Rapidly cooling lava Slowly cooling magma
Small crystals Large crystals
Extrusive rocks Intrusive rocks
Granite - Intrusive
Rhyolite - extrusive
CLASSIFYING IGNEOUS ROCKSBY MINERAL COMPOSITION
Mineral composition of Granite
Uses of Igneous Rocks• Granite - For buildings & monuments – Egyptians used for
statues over 3,500 years ago.• Basalt – crushed for gravel in construction.• Pumice – used for polishing.• Obsidian – used for ancient tools.
Igneous rocks ALL were formed from magma or lava
They are classified by origin, texture and mineral composition
They may form ON or BENEATH Earth’s surfaceExtrusive rock: From lava on the surface Intrusive rock: From magma that hardened under the surface
Since they are hard, dense and durable they have been used for tools and building materials.
IN SUMMARY…
SEDIMENTARY ROCKS
Sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation.
TYPES OF SEDIMENTARY ROCKS
Clastic – particles are squeezed together.
Organic – remains of plants and animals.
Chemical – solutions evaporating
Shale
Conglomerate
Sandstone
coal limestone
Rock salt
Sediment is small, solid pieces of material that come from rocks or living things
Series of processes: Erosion (water/wind), deposition (sediment lands somewhere), compaction (presses sediment together with weight/pressure), cementation (dissolved minerals crystallize and glue particles of sediment together)
Clastic rocks: formed when rock fragments squeezed together (sandstone)
Organic rocks: remain of plants/animals deposited in thick layers. (coal)
Chemical rocks: minerals dissolved in a solution crystallize (limestone)
IN SUMMARY…
METAMORPHIC ROCKS
Heat and pressure deep beneath Earth’s surface can change any rock into metamorphic rock.
FOLIATED VS. NONFOLIATED
Two categories foliated: grains arranged in parallel layers or bands non-foliated: mineral grains arranged randomly.
Heat and pressure DEEP beneath Earth’s surface can change ANY rock to a metamorphic rock.
When changed into metamorphic rock it changes its appearance, texture, crystal structure and mineral content
High temperatures/pressure can change minerals into other minerals!
Metamorphic rock classified by the arrangement of grains that make up the rock Parallel layers : foliated Random grains: nonfoliated
Used for building and sculpture ( marble/slate) Marble formed from limestone subjected to heat/pressure below
Earth’s surface
IMPORTANT CONCEPTS
Rocks are continuously built, destroyed and changed in the crust.
Example: Igneous rock granite formed beneath surface Forces of mountain building push granite upward
(forming mountain) Slowly, water/wind wear away granite Granite particles become sand, carried by streams to the
ocean Over millions of years sandy layers pile up on ocean floor Slowly, sediment changes to sandstone (sedimentary
rock) Over time, sandstone is buried Heat/pressure change rock’s texture Sandstone changed into metamorphic rock : quartzite
IMPORTANT CONCEPTS