Earth's Rock Cycle

• The Earth's crustal rocks are constantly changing form through the rock cycle
• The rock cycle is propelled by Earth's internal heat and solar-powered hydrological cycle
• Earth's active rock cycle is due to a hot core, a thick atmosphere, and liquid water

Rock Cycle Explained

• Magma cools to form new minerals and igneous rocks
• Magma cools slowly within the crust to form intrusive igneous rock
• Lava cools quickly on the surface to form extrusive igneous rock
• Mountain building exposes rocks to weathering agents like water, wind, ice, and gravity
• Weathering breaks rocks physically and chemically, creating sediments
• Sediments are transported and deposited in various environments, eventually becoming buried
• At depth, sediments compress and cement into sedimentary rock
• Deeply buried rocks undergo metamorphism due to increased heat, pressure, and tectonic stress
• Metamorphism alters the stability, fabric, and texture of pre-existing minerals, forming metamorphic rock

Igneous Rock

• Magma temperature ranges from 800° to 1600°C, depending on its origin within the mantle
• Intrusive igneous rock cools slowly within the crust and is also called plutonic rock
• Extrusive igneous rock cools quickly on the surface and is also called volcanic rock

Igneous Rock Classification

• Igneous rocks are classified by composition and texture
• Composition is based on the minerals present
• Bowen’s Reaction Series outlines the crystallization sequence of silicate minerals from cooling magma

Igneous Rock Composition

• Igneous rock composition is divided into ultramafic, mafic, intermediate, and felsic categories
• These categories reflect the amounts of silica, potassium, sodium, calcium, iron, and magnesium in the rock
• Mafic rocks are high in magnesium (Mg) and iron (Fe), containing ferromagnesian minerals
• Felsic rocks are enriched in sodium-rich plagioclase, potassium feldspar, and silica (SiO2) as quartz

Igneous Rock Composition Types

• Ultramafic rocks contain mostly olivine, with some pyroxene and calcium-rich plagioclase and are rarely found on Earth's surface
• Mafic rocks are abundant in ferromagnesian minerals (olivine and augite) and calcium-rich plagioclase feldspar, making up the oceanic crust
• Intermediate rocks have roughly equal amounts of light and dark minerals, such as plagioclase feldspar and hornblende, associated with convergent plate boundary volcanoes
• Felsic rocks contain mostly light-colored minerals like feldspar and quartz, with minor dark minerals, dominating the continental crust

Igneous Rock Texture

• Intrusive (plutonic) rocks cool slowly deep within the crust, resulting in coarse-grained or phaneritic textures with visible mineral crystals
• Extrusive (volcanic) rocks cool quickly on the surface, leading to fine-grained or aphanitic textures with tiny crystals
• Rapid cooling may result in volcanic glass like obsidian

Common Igneous Rocks and their Characteristics

• Granite: Felsic composition, phaneritic texture, intrusive
• Rhyolite: Felsic composition, aphanitic texture, extrusive
• Diorite: Intermediate composition, phaneritic texture, intrusive
• Andesite: Intermediate composition, aphanitic (often porphyritic) texture, extrusive
• Gabbro: Mafic composition, phaneritic texture, intrusive
• Basalt: Mafic composition, aphanitic texture, extrusive
• Peridotite: Ultramafic composition, phaneritic texture, intrusive
• Komatiite: Ultramafic composition, aphanitic texture, extrusive

Sedimentary Rocks

• Sediments turn into sedimentary rocks when buried under hundreds of meters of other sediments
• Sediments come from the weathering of pre-existing rocks exposed at or near the surface

Sedimentary Rock Cycle

• Pre-existing rocks are exposed to weathering and erosion
• Weathering involves exposure to wind, water, ice, and gravity
• Erosion removes weathered material
• Agents cause physical disintegration and chemical changes
• Water is the dominant agent, altering mineral chemistry
• Sediment particles and ions in water are produced
• Sediment is transported and deposited
• Burial, compaction, and cementation (diagenesis) lithify sediment into rock
• Ions in solution can cement sediment, support life, or precipitate out

Sedimentary Rocks Classification

• Sedimentary rocks are classified as clastic, chemical, biochemical, or organic

Clastic Sedimentary Rocks

• Clastic sedimentary rock consists of cemented sediment pieces (clasts) from weathered bedrock
• Clastic sediment is referred to as "siliciclastic," derived from silicate minerals of igneous rock
• Clastic rocks are named based on the size and composition of the clasts

Clastic Sedimentary Composition

• Conglomerate: coarse-grained with rounded gravel-sized clasts
• Breccia: coarse-grained with angular gravel-sized clasts
• Quartz sandstone: mainly sand-sized quartz grains
• Arkose sandstone: mainly sand-sized feldspar grains
• Greywacke: dark, poorly sorted angular grains in a clay matrix
• Siltstone: primarily silt-sized particles
• Shale: fine-grained with clay minerals and silt
• Claystone: largely clay, non-fissile

Chemical Sedimentary Rocks Formation

• Chemical sedimentary rock is formed by processes not directly involving mechanical weathering and erosion
• Inorganic chemical sedimentary rock forms from minerals precipitated from ions dissolved in a solution
• Concentration, dissolved gasses, temperatures, or pressures cause minerals to crystallize

Biochemical Sedimentary Rocks Formation

• Biochemical sedimentary rock is formed from shells and bodies of underwater organisms
• Living organisms extract chemical components from the water and use them to build shells and other body parts
• Rocks are commonly made of calcite or silica

Organic Sedimentary Rocks Formation

• Organic sedimentary rock contains the remains of organic material
• The source materials are plant and animal remains that are transformed through burial and heat
• Coal, oil, and methane are examples of organic sedimentary rocks

Common Chemical, Biochemical and Organic Sedimentary Rocks

• Fossiliferous limestone: limestone with abundant fossils
• Oolitic limestone: limestone formed from ooids with concentric layers of calcium carbonate
• Micrite: limestone formed of calcareous particles, recrystallized calcareous mud
• Chalk: soft, white limestone composed of minute calcite shells
• Travertine: limestone deposited by mineral springs, especially hot springs
• Crystalline limestone: carbonate sedimentary rock composed of calcite precipitation
• Dolostone: contains a high percentage of the mineral dolomite
• Chert (and Flint): hard, fine-grained quartz
• Rock gypsum: composed of gypsum from seawater evaporation
• Rock salt: composed of halite from seawater evaporation
• Bituminous coal: organic sedimentary rock formed from peat bog material

Metamorphic Rocks

• Metamorphism is the change within a rock due to different conditions from its original formation
• Rocks are deeply buried where they're subjected to higher temperatures and pressures
• Involves the recrystallization of minerals plus the formation of new minerals and different textures

Metamorphism Causes

• Metamorphism results from tectonic forces during mountain building episodes
• Plate collisions introduce tremendous stress and heat

Metamorphism Types

• Regional metamorphism: occurs over a wide area of the crust resulting from tectonic plate collisions
• Alters continental crust, oceanic crust, and sedimentary rock
• Contact metamorphism: affects pre-existing rock by baking them through contact with molten rock material
• Occurs through intrusion of magma or extrusion of lava on the surface

Metamorphism Factors

• The mineral composition of the parent rock
• The temperature at which metamorphism takes place
• The amount and type of pressure during metamorphism
• The types of fluids (mostly water) that are present during metamorphism
• The amount of time available for metamorphism

Metamorphism Protolith

• The protolith is the rock that exists before metamorphism
• The critical component of the parent rock is its mineral composition
• Certain minerals may become unstable and begin to recrystallize in size, orientation or into completely new minerals

Metamorphism and Temperature

• Minerals gain stability as temperature cools
• Quartz is stable under all surface environmental temperatures up to ~1800°C
• Clay minerals are stable up to about 150° to 200°C, then transform into micas
• Feldspar is stable up to approximately 1200°C

Metamorphism and Pressure

• Pressure is the force exerted on the protolith by burial and/or tectonic stresses
• Confining pressure results in equal pressure on all sides causing chemical reactions and new minerals to form
• Differential stress: unequal balance of forces on the protolith in one or more directions, related to tectonic movement
• Differential stress modifies the parent rock at a mechanical level, changing the arrangement, size, and/or shape of the mineral crystals
• Foliation results

Metamorphism and Fluids

• Water is the main fluid within rocks of the crust
• Water assists in metamorphic mineral growth and increases the rate at which metamorphic reactions take place

Metamorphism and Time

• Metamorphic reactions take place at very slow rates
• Growth of new minerals during metamorphism is slow, approximately 1 millimetre per million years

Metamorphic Rock Classification

• Metamorphic rocks are classified by texture and composition
• Foliated rocks are formed in an environment subjected to differential stress
• Non-foliated rocks are either not subjected to directed pressure or the dominant mineral doesn't display alignment

Foliated Metamorphic Rocks

• Slate: fine-grained exhibiting slaty cleavage
• Phyllite: fine-grained where platy chlorite and mica minerals have grown larger
• Schist: minerals are visible as individual crystals
• Gneiss and Migmatite: mineral banding with dark and light bands

Non-Foliated Metamorphic Rocks

• Non-foliated textures do not display alignment of mineral grains
• Typically composed of just one mineral
• Amphibolite: result of metamorphism of a mafic igneous protolith
• Greenstone: largely composed of the green chlorite mineral plus other typically green metamorphic minerals, epidote and serpentine
• Quartzite: protolith is quartz sandstone
• Marble: metamorphosed limestone (or dolostone) composed of calcite (or dolomite)