GEOG203-MaterialNotes 10.03.23

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Oct 30, 2023

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GEOG203: Environmental Systems – Material Notes: Oct 3 rd Christopherson et al. pp. 355-362 Earth Materials and the Rock Cycle - Minerals are the building blocks of rocks - Mineral: an inorganic, or non-living, natural solid compound having a specific chemical formula and usually possess a crystalline structure o Every mineral has its own characteristic: colour, texture, crystal shape, and density - Rock - an assemblage of minerals bound together (ie. granite; which is a rock containing three minerals) ; or a mass composed of a single material (such as rock salt); or of undifferentiated material; or even solid organic material (such as coal) - 3 General Types of Rock o Igneous: formed from molten material o Sedimentary : formed from compaction or chemical processes o Metamorphic : altered by heat and pressure Igneous Processes - Igneous rock forms from molten rock beneath earth’s surface ( magma ) - Make up approx. 90% of earth’s crust Igneous Environments - Since magma is fluid, highly gaseous, and under a lot of pressure – it either intrudes or extrudes o Intrusive igneous rock = magma that intrudes into crustal rocks, cooling and hardening below the surface o Extrusive igneous rock = magma that extrudes onto the surface as lava and cools  Results from volcanic eruptions and flows - Location and rate of cooling are determinants for the crystalline texture of a rock o Whether it is made of coarser or finer materials o * Texture indicates environment - Slower cooling of magma : more time for formation = coarse grained rocks ( granite ) - Faster cooling of lava : forms finer grained rocks ( basalt ) - Basalt is the most common extrusive igneous rock; makes up a bulk of the ocean floor (71% earth’s surface) - Really rapid cooling results in glassy rock , like obsidian , or volcanic glass ; Pumice

Igneous Rock Classification - The mineral composition of a rock, provides information about the source of the magma that formed it, impacting its physical characteristics Igneous Landforms - When igneous rocks are uplifted by exogenic processes; air, water, and ice sculpt them into landforms Sedimentary Processes - Loose clasts (grains or fragments) become cemented together, as a result of solar energy and gravity o the clasts that form rock come from many different places:  weathering and erosion of existing rock  accumulation of shells on the ocean floor  accumulation of organic matter from ancient plants  precipitation of minerals from water solution - Categories of sedimentary rocks: o clastic , bio-chemical , organic , and chemical Clastic Sedimentary Rocks Felsic Igneous Rocks name derived from: feldspar and silica - High in silicate materials - Low melting points - Rocks formed from felsic minerals are typically lighter in colour and less dense - Example: granite Mafic Igneous Rocks - Derived from magnesium and iron - Lower in silica; higher in magnesium & iron - High melting points - Rocks formed from mafic minerals are typically darker in colour and more dense than felsic minerals - Example: basalt

- formed by an extensive process 1. weathering and erosion disintegrate and dissolve existing rock into clasts 2. transportation by the elements, carries these rock particles across landscapes, now referred to as sediment 3. transport carries the material to low energy sites where the sediment is deposited ; deposition is when sediment settles out and becomes material dropped along river channels, beaches, ocean bottoms – where it is eventually buried 4. loose sediment is hardened into solid rock ( lithification ); buried sediments are compacted as the weight of overlying materials squeezes out the water and air between clasts 5. minerals act as the cement to fuse the clasts 6. following lithification, the size classes, combined with their composition, sorting and cement characteristics determine the common sedimentary rock types Chemical Sedimentary Rocks - formed from the shells of organism that contain calcium carbonate ( biochemical process ) or dissolved minerals that precipitate out of water solutions ( chemical process ) – subsequently building up to form rock - chemical precipitation: formation of a separate solid substance from a solution (i.e. water evaporates and leaves behind salts) - most common chemical sedimentary rock: limestone o most common form is the biochemical limestone from marine organic origins  when organisms extract dissolved CaCO 3 from seawater to construct solid shells, and go onto die the shell material builds up on the ocean floor and is lithified to become limestone - clastic and chemical sedimentary rocks become deposited in layered strata that form an important record of past ages; using the principle of superposition, scientists use the stratigraphy (ordering of layers), thickness, and spatial distribution of the strata to determine the age and origin of rocks Metamorphic Processes - transformed (physical/chemical changes under pressure or increased temp.) igneous or sedimentary rock - more compact than the original rock, thus more resistant to weathering and erosion o four processes of metamorphism:  heating ; when applied to rock, atoms in the mineral break their bonds, move, and form new bonds  pressure ; mineral structures change as atoms become more closely packed  heating & pressure (combined); original mineral assemblance becomes unstable and subdues to change

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 compression and shear ; compressed by overlying weight and subject to shear when one part of the mass moves sideways relative to another part - all of these processes change the shape of the rock, which changes the interior mineral alignments