What is a Rock? • Naturally-occurring mixtures of minerals, mineraloids (no crystals), or organic matter.
Types of Rocks… • The three main kinds of rock are igneous, sedimentary and metamorphic rock. • Igneous rock: forms when magma/lava cools and hardens • Sedimentary rock: forms when sediments are buried, compacted & cemented together • Metamorphic rock: forms when existing rock is subjected to great heat & pressure over a long period of time
What is the difference between a rock and a mineral? • Rocks are made up of ONE or MORE minerals.
Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling • Rocks can change to and from the three types
What is the process through which rocks change? • The Rock Cycle—earth materials change back and forth among the different types of rocks
IGNEOUS SEDIMENTARY METAMORPHIC Weathering, Erosion, Compaction, Cementation Recrystallization Melting, Solidification Melting, Solidification Recrystallization Weathering, Erosion, Compaction, Cementation
How are rocks redistributed? • The core, mantle, & crust are one giant rock recycling machine
Igneous Rocks • “Ignis” = Latin for “fire” • Formed from the cooling of either magma or lava • The most abundant type of rock • Classified according to their origin and composition • Igneous Rocks come from magma/lava cooling down.
ORIGIN— Where rocks are formed • Below ground = from magma (intrusive igneous rock) • Usually have LARGE crystal grains (they cooled slowly) Cooling could have taken hundreds of years.
Above ground = from lava (extrusive igneous rock) • Usually have SMALL or NO crystals (they cooled too quickly)
Basaltic Igneous Rocks—made from lava/magma that is low in silica, rich in iron and magnesium. Rocks are dark-colored.
Granitic Igneous Rocks—made from magma/lava high in silica and oxygen. Rocks are light-colored.
Andesitic Igneous Rocks—have a composition between basaltic and granitic.
Sedimentary Rocks • Formed from sediments (rock fragments, mineral grains, animal & plant remains-shells, bones, leaves, stems) that are pressed or cemented together or when sediments precipitate out of a solution.
Sedimentary Rocks • These sediments are moved by wind, water, ice or gravity then deposited into layers. • Sedimentary rocks represent 7% of the Earth’s crust, but they cover 70% of the Earth’s surface. • Sedimentary rocks are fossil-carrying rocks.
What turns sediments into solid rock? • Water or wind breaks down and deposits sediment (erosion & deposition) • Elements of Erosion are heat, cold, rain, waves, and grinding ice.
At first sediments fit together loosely, over long periods of time, thick layers build up. Because of the heavy layers, the upper layers press down on the layers below them, causing Compaction.
Dissolved minerals flow between the particles and cement them together (cementation)
How can sedimentary layers help us understand the age of fossils? • As sedimentary rocks are deposited, they form horizontal layers • Scientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.
3 Types of Sedimentary Rocks: • Clastic (also called Detrial)—made of broken pieces of other rocks. Formed when rock fragments are squeezed together.
Clastic-Sedimentary Rocks • Shale: Formed from tiny particles of clay compacted together. • Sandstone: Forms from the compaction and cementation of small particles of sand.
Clastic-Sedimentary Rocks • Conglomerate: Formed from fragments of various sizes of rocks and pebbles. Fragments are rounded because they have been worn along riverbeds. • Breccia: Fragments are jagged with sharp edges. Formed from various size of rocks and pebbles.
3 Types of Sedimentary Rocks: Organic—remains of plants and animals are deposited in thick layers • Organic refers to substances that once were part of living things or were made by living things which contain calcite or calcium carbonate. (Can be tested by using acid)
Organic-Sedimentary Rocks • Coal: Remains of swamp plants buried in water or by volcanic ash. • Limestone: Formed by hard shells of once living things such as coral, clams, oysters, and snails. When they die their shells pile up and are covered by other sediments compacting and cementing them.
Types of Limestone • Chalk-can be naturally occurring and in rock form. • Coquina-made of large fragments of shells.
3 Types of Sedimentary Rocks: • Chemical—minerals dissolved in lakes, seas, or underground water. Can occur when lakes evaporate.
Chemical-Sedimentary Rocks • Rock Salt: Made of the mineral halite. • Gypsum: Formed by evaporation in dry climates.
Metamorphic Rocks • Rocks that have changed due to intense temperature and pressure • “Meta” means “change” and morphosis means “form” in Greek • Igneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks
What occurs in the Earth to change these rocks? • Pressure from overlying rock layers • High heat, but not enough to melt the rock • Rocks may be flattened or bent or atoms may be exchanged to form new minerals.
*You can think of metamorphic rocks as a squished peanut butter & jelly sandwich in your lunch.
Where do metamorphic rocks usually form? • Where magma intrudes relatively cool rock • Near colliding plates (near mountain ranges) • Places that are covered miles thick with other rock causing pressure • When hot water intrudes rock • Where a meteorite strikes Earth (rare) • Where lightning bolts strike rocks (rare)
How are metamorphic rocks classified? Look at Pages 162-163 in your books • Foliated—mineral grains are flattened and line up in parallel bands • Example: gneiss formed from rearrangement of minerals in granite into bands
How are metamorphic rocks classified? • Non-Foliated—No bands are formed • Example: marble formed from limestone
Rocks Transformed Limestone Marble Shale Slate
Rocks Transformed Sandstone Quartzite Gneiss or Mudstone Schist
Say you have an unknown rock how do you classify it? • Color: Like with minerals, color alone does not provide enough information to identify a rock.
Say you have an unknown rock how do you classify it? • Texture can be very useful. Look at and feel the rocks surface. • Some are smooth and glassy others are rough and chalky. • Grain Size: Large or Small • Grain Shape: Fine Grained or Jagged • Grain Patterns: Flat Layers, Wavy, banded, or random. • No Visible Grain: Some cool to fast to have grains.