GY1004 Part 1 (Weeks 1-5) Weathering, Soils and Landscape Weathering Pedogenesis Denudation Global scale variations
Weathering, Soils and Landscape Weathering Rocks and minerals Physical weathering processes Chemical weathering processes Weathering products and process controls
Weathering, Soils and Landscape Soils The soil system and soil properties Soil processes, types and patterns
Weathering, Soils and Landscape Erosion and Landscape Agents and landscapes of erosion and deposition Rates of denudation Uplift and denudation
Multiple Choice test based on Lectures 1-10 Monday 1 st March 2004
PowerPoint presentations can be viewed at www.geog.le.ac.uk/staff/dmp6/teaching
Weathering: An introduction Weathering - The chemical alteration and physical breakdown of rock material at or near the earth’s surface.
The significance of weathering Weathering is often a precursor to erosion by rivers, winds, glaciers and mass movements Geomorphologists study the development of landscapes and are concerned with rates of weathering processes, the nature of the weathered material and the landforms that result
The significance of weathering Weathering also gives rise to specific landforms Bornhardts, Rio Karst, China Finger of God, Namibia
The significance of weathering Weathering produces regolith, the parent material of soils. Soil scientists are interested in the way weathering contributes to soil properties and the release and movement of nutrients A terra rossa soil
Weathering 1)Rocks and minerals 2)Chemical weathering processes 3)Physical weathering processes 4)Weathering products and process controls
Lecture 1 Rocks and minerals Minerals – the building blocks of rocks The atomic structure of matter Rock forming minerals Rocks and rock types
What is a mineral? A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition. Must be found in nature A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition. Atoms are arranged in an orderly, repeated 3d array A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition. Excludes organic substances that make up plant and animal bodies A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition. The combination of its chemical composition and the arrangement of its atoms in its internal structure makes each mineral unique A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition. Olivine Quartz
What is a rock? Rocks are made up of varying assemblages of minerals Minerals, therefore, are the building blocks of rocks Calcite Limestone outcrop El Torcal de Antequera, Spain orthoclase plagioclase quartz hornblende biotite Granite The minerals of Granite
Elements and atoms Elements are the most fundamental substances into which matter can be separated and analysed by ordinary chemical means An atom is the smallest unit of an element that retains the physical and chemical properties of that element. Eight most abundant elements in Earth’s crust - oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium.
The structure of the atom Protons Neutrons Electrons Charge +1 0 Mass 1 1/1836
Atomic number, atomic mass and isotopes Atomic number (Z) – the number of protons in the nucleus of an atom Hydrogen (Z = 1)Carbon (Z = 6)
Atomic number, atomic mass and isotopes Atomic mass (mass number; A) is the mass of the atom. It is equal to the number of protons and neutrons in the nucleus. Hydrogen (A = 1)
Isotopes are elements with different numbers of neutrons in the nucleus. Isotopes have the same atomic numbers (no. of protons), but different mass numbers (numbers of protons and neutrons). ProtonsNeutrons Carbon 12 6 6 Carbon 13 6 7 Carbon 14 6 8
Why do minerals form? Na Cl Sodium atom: 1 electron in outer shell Chlorine atom: 7 electrons in outer shell Chemical reaction Na + Cl - Sodium loses 1 electron to become sodium ion Chlorine gains 1 electron to become chlorine ion Electrical attraction Cl - Na + Compound, sodium chloride (NaCl), formed by electrical attraction between Na + and Cl -
Chemical bonds Electrical forces of attraction between electrons and protons IONIC– between ions of opposite charge - most common mineral bond COVALENT – between ions that share electrons - stronger than ionic bonds
When do minerals form? Temperatures below freezing/melting points Precipitation during evaporation
Rock forming minerals Silicates - the most abundant and important rock forming mineral - composed of oxygen and silicon mostly in combination with the cations of other elements (e.g. Na, Ca, Mg, K) orthoclase plagioclase quartz hornblende biotite
Rock forming minerals Carbonates - minerals made up of carbon and oxygen in the form of the Carbonate ion (CO 3 ) and in combination with calcium and magnesium Calcite
Rock forming minerals Oxides - compounds of oxygen and metallic cations such as hematite (Fe 2 O 3 – iron oxide) Hematite
Rock forming minerals Sulphides and sulphates - compounds of the sulphide (S 2 - ) and sulphate (SO 4 - ) ion e.g. iron pyrite (FeS 2 fools gold) and anhydrite (CaSO 4 ) iron pyriteanhydrite
Rocks and rock properties Texture – the sizes, shapes and spatial arrangement of its crystals and grains Mineralogy – the kinds and proportions of the minerals that make up the rock
Igneous rocks Common minerals *Quartz *Feldspar *Mica *Pyroxene *Amphibole *Olivine * silicate minerals Crystals form from Magma cooling and settle to floor of chamber Crystals from early cooling accumulate
Weathering and erosion Sedimentary rocks Burial and lithification into sedimentary rock Ocean transport and deposition by currents and chemical precipitation Land transport and deposition by water, wind, ice
Sedimentary rocks Chemical – calcite, gypsum, halite Biogenic – limestone, dolomite, chert Clastic – sandstones, mudstones and conglomerates silicates, e.g. quartz, clay minerals and feldspar carbonates, sulphates and chlorides carbonates Lithification – compaction and cementation
SUMMARY Minerals Minerals are the building blocks of rocks Minerals are naturally inorganic solids with specific crystal structures and chemical compositions. There are about 3500 minerals, but about 30 are responsible for about 99% of the volume of the earth’s crust.
SUMMARY The atomic structure of matter Minerals are constructed of atoms, the small units of matter that combine in chemical reactions An atom is composed of a nucleus of protons and neutrons surrounded by electrons travelling in orbitals (shells) around the nucleus. The atomic number of an element is the number of protons in its nucleus The atomic mass of an element is the sum of the masses of its protons and neutrons.
When an mineral crystallises, atoms or ions come together in the proper proportions to form a crystal structure – an orderly three dimensional geometric array in which the basic arrangement is repeated in all directions. SUMMARY How do minerals form? Chemical substances react with each other to form compounds either by gaining or losing electrons to become ions or by sharing electrons. Either way, the atoms achieve stable configurations of electron shells. The atoms or ions of a mineral are held together by ionic or covalent bonds
SUMMARY The rock forming minerals Silicates are the most abundent minerals in the Earth. They are composed of tetrahedra of silicon and oxygen atoms linked in various ways Carbonate minerals are made up of carbonate ions bonded to calcium and/or magnesium. Oxide minerals are compounds of oxygen and metallic elements. Sulphate and sulphide minerals are structures made up of sulphur atoms in combination with metallic elements.
SUMMARY Rocks Rock properties are defined by mineralogy (the kinds and proportions of the constituent minerals) and texture (the sizes, shapes and spatial arrangement of its crystals or grains). The mineralogy and texture of a rock are determined by the geologic conditions, including chemical composition, under which it formed Igneous rocks are formed by the crystallisation of magma as it cools; Sedimentary rocks are formed by the lithification of sediments/precipitates; Metamorphic rocks are formed by the alteration in the solid state of igneous, sedimentary or other metamorphic rocks by heat and or pressure.