Rocks

Rocks - Aggregate (mixture) of one or more minerals

Minerals - Naturally occurring, inorganic, crystalline solid with a defined chemical composition

Rocks:

Orthoclase Feldspar

Quartz

Biotite

Plagioclase Feldscar

Felsic - Silica rich rocks, make the rock lighter

Mafic - Magnesium and iron rich rocks, makes the rocks darker

Ultramafic - Magnesium and iron rich rocks, low silica, makes rocks greenish

Texture:

Crystalline - made of interlocking minerals that grew together, forming in high temp. environments by crystallization of magma, metamorphism, or precipitation from hot water

Clastic - pieces derived from older weathered and eroded rock

Rock Classification

Igneous - made from magma cooling to the point of hardening (think obsidian from Minecraft)

• Extrusive igneous rocks - hardens at Earth’s surface (Above), rapid cooling, fined grained or small crystals, Aphanitic Rocks

• Intrusive igneous rocks - hardens within the Earth (Below), slow cooling, coarse grain or coarse crystals, Pheniyitic Rocks

• Magma cooling within Earth produces intrusive igneous rocks

• Lava cooling at or near Earth’s surface produces extrusive igneous rocks

Cooling Times

• Ash: minutes

• Lava flow: days - months

• Shallow sill: weeks - months

• Deep sill: months - years

• Deep pluton: centuries - millions of years

Texture Types

Coarse grained: Intrusive, Phaneritic

Fine grained: Extrusive, Aphanitic

2 textures: Intrusive then Extrusive, Porphyritic

No minerals: Extrusive, Glassy

Vescular (Bubble holes): Extrusive

Welded and Non-welded

How Do We Get Igneous Rock of Different Compositions?

Magmatic Differentiation is a process where rocks of varying compositions can come up from a uniform parent magma

• occurs because different minerals crystallize at different temperatures.

• Last minerals to melt: first minerals to crystallize from a cooling magma

Sedimentary - made from particles that settle through water or air

• Formed from different rocks

• Sediment = pieces that result from the breakdown of rock

• 2 types: Pieces of broken rocks and Minerals that form when dissolved ions bond together

Metamorphic - transformation of sedimentary rocks and/or igneous rocks are exposed to extreme pressure from weight of rocks/heat

• Can change mineral composition and texture of all types of rocks

Rock Cycle

1. Magma crystallizes and forms igneous rock

2. Igneous rock can weather, erode and de-position and form sediment

3. Sediment due to compaction and cementation can form sedimentary rock

4. Sedimentary rock when heated or pressured can form into metamorphic rock

5. Metamorphic rock when melted can form back into magma

Igneous and sedimentary rocks can also melt and form back into magma

Igneous rocks, due to heat and pressure, can form into metamorphic rocks

Metamorphic and sedimentary rocks, when weathering, eroding, and/or de-positioning, can form or go back to sediment

Rocks and Plate Tectonics

Divergent Plate forms:

Igneous rocks (as plates move apart)

Convergent Plate Boundaries (With Subduction) forms:

All 3 types of rocks (variety of ennvorinments)

Continent Convergent Plate Boundaries (No Subduction) form:

Sedimentary and metamorphic rocks (from formation of mountains)

No Plate Boundary (Passive Margins, Ex. East Coast of NA) form:

Sedimentary rocks (sediment deposites in the ocean)

Hot Spots form:

Igneous rocks (lava/magma cooling)

Sedimentary rocks are the rocks on the Earth’s crust and the first layer, while metamorphic rocks and igneous rocks are under the crust in the bottom layer, making up about 75%.

Volcanoes

• Hill or mountain constructed from the accumulation of erupted lava and pyroclasts around a central vent

Volcanic Eruptive Products include:

Pyroclasts - Magma rising close to surfaces dropping pressure, volatiles (gases) can be released with explosive force that shatters the lava and surrounding rock producing shattered pieces

Ex. Cinders (Gravel sized pieces of basalt)

Bombs - Fragments ejected as blobs of lava that cool in flight and become rounded or chunks torn loose from previously solidified volcanic rock

• larger than 64mm

Sedimentary Rocks

Why Study Them?

1. Most common rocks on Earth’s ssurface (70%)

2. Most of our history are from sedimentary rocks

• Paleoenvironments, paleogeography: fossils are made of sedimentary rocks

3. Economic - world’s economic deposites are sedimentary rocks

4. It’s Practical - engineering applications, groundwater,

Types of Sediment

• Clastic (from Clasts)- from broken pieces of original rock from physical weathering (erosion, etc) Most common

• Chemical - ions dissolved in water from chemical weathering

• - Salt for example when saltwater dissolves through the ground, it leaves the salt behind to wash onto the shore, hence creating sediment

• Biologic (biochemical) - skeletal debris from organisms (shells, etc)

• Organic - form from once living organisms

Weathering - Process of converting rock into sediment and forming soils (Breaks Rocks)

Physical (Mechanical) - Breaking larger rocks into smaller rocks and not changing minerals

Types of Physical Weathering

Frost Wedging - Water expanding when freezing which expands fractures in the rock and can push blocks to expansion (Think about when water below freezing during the winter hits our roads and breaks up the concrete and cracks on our roads appear)

Salt Weathering (Mineral Wedging) - Saline water gets into cracks

Root Wedging - When roots expand from growth, it breaks the rock from the active growth

Exfoliation - When rocks form deep in the Earth and form under a lot of pressure. As overlying rock is removed by erosion. the amount of pressure decreases and expands vertically/up. Forms cracks that are parallel to surface.

Chemical - Minerals reacting with air and water. Decomposes rocks, soil, other Earth materials through chemical reactions involving water

Types of Chemical Weathering

Dissolution - Minerals dissolving, Ca, Mg, K,

• pH Scale - How acidic a acid is (1-14: 1, most acidic, to 14, least acidic)

Oxidation: Mineral rust, reacting with oxygen, Fe combining with O to make iron oxides

Results of Weathering

Rough becomes smooth

Soil gets sediment

Rock/Mineral Type

Certain minerals break down more easily depending on bond type and reactivity

Exposed Surface Area

More surface area leads to more exposure to weather (cracks lead to faster weathering)

Surface Area - Area x # of sides

Climate

Chemical reactions happen faster at warmer temperatures

Mafic is less resistant to weathering

Silicic is more resistant to weathering

Erosion (mass wasting) - Transporting rock/sediment from one place to another. Done by flowing water air ice or gravity

Currents are the main transportation of sediments. Strength of current oversees the max size of particles that can be transported

Strong - large particles

Weak - small particles

Clastic Sedimentary Rocks

Consist of mineral grains, rock fragments, cementing material

• Clastic particles are dissolved ions journey to a sedimentary basin

• Currents are main mode of transportation for sediments

• Size of particles decrease as you travel away from the source

• Rounder particles traveled farther

• Sediment starts angular, they transport and get smoother due to change

Clastic Sedimentary Rocks:

Breccia - coarse, angular rock fragments

Conglomerate -

Shale/Mudstone - Fine coarse composed of silt and clay

Biologic - From sediments from shells of once living organisms.

Limestone - made almost entirety of Calcite

Organic Sedimentary Rocks -

Desposition When Travelling Stops

• Transported until current is not strong enough to carry them then deposited

• Deposition = settling out of transporting fluid

Lithification: How to Make a Rock

• Lithification transforms loose sediment into solid rock via compaction and cementation

• Compaction burial increases pressure, squeezes out air and water, and compacts grains (Large Particles)

4 Types of Natural Cement:

1. Calcite: a common cement in sandstone and other sedimentary rocks. It holds grains together moderately well, but it is easily redissolved, so a calcite-cemented sandstone may become crumbly.

2. Silica: acts as a cement in some sandstone and other sedimentary rocks. It forms a strong cement that can tightly bind grains and form a tough, resistant rock.

3. Clay minerals can cement together larger grains, including sand. They may have be deposited with the sediment or formed from the weathering of feldspar

4. Iron oxide minerals, like hematite, precipitate from water as a natural cement between the grains. Iron oxide minerals commonly give sediment deposited on land a reddish color

Classifying Sedimentary Rocks

Classified by size of sedment (grain size)

Grain Size - measure of the size of fragments or grains

Sizes are from very coarse - very fine (gravel, sand, silt, clay)