GY1004 Principles of Physical Geography B
Dr Mark PowellRoom F44
DEPARTMENT OF GEOGRAPHY
GY1003
GY1004 Part 1 (Weeks 1-5) Weathering, Soils and
Landscape
Weathering
Pedogenesis
Denudation
Global scalevariations
Weathering, Soils and Landscape
WeatheringRocks and mineralsPhysical weathering processesChemical weathering processesWeathering products and
process controls
Weathering, Soils and Landscape
SoilsThe soil system and soil
propertiesSoil processes, types and
patterns
Weathering, Soils and Landscape
Erosion and LandscapeAgents and landscapes of
erosion and depositionRates of denudationUplift and denudation
Multiple Choice test based on Lectures 1-10
Monday 1st 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
CalciteLimestone outcrop
El Torcal de Antequera, Spainorthoclase plagioclase
quartzhornblende
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
-1
Mass
1
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)
Atomic number, atomic mass and isotopes
Atomic number, atomic mass and isotopes
Atomic number, atomic mass and isotopes
Atomic number, atomic mass and isotopes
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).
Protons Neutrons
Carbon 12 6 6
Carbon 13 6 7
Carbon 14 6 8
Why do minerals form?
Na
Cl
Sodium atom:1 electron inouter shell
Chlorine atom:7 electrons inouter shell
Chemicalreaction
Na+
Cl-
Sodium loses 1 electronto become sodium ion
Chlorine gains 1 electronto become chlorine ion
Electricalattraction
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
How do minerals form?E.g. Diamond
How do minerals form?E.g. Diamond
How do minerals form?
E.g. Diamond
When do minerals form?
Temperatures below freezing/melting points
Precipitation during evaporation
Rock forming mineralsSilicates - 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
quartzhornblende
biotite
Rock forming minerals
Carbonates- minerals made up of carbon and oxygen in the form of the Carbonate ion (CO3) and in combination with calcium and magnesium
Calcite
Rock forming minerals
Oxides- compounds of oxygen and metallic cations such as hematite (Fe2O3 – iron oxide)
Hematite
Rock forming minerals
Sulphides and sulphates
- compounds of the sulphide (S2-) and
sulphate (SO4-) ion e.g. iron pyrite (FeS2
fools gold) and anhydrite (CaSO4)
iron pyrite anhydrite
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 rocksCommon minerals
*Quartz*Feldspar*Mica*Pyroxene*Amphibole*Olivine
* silicate minerals
Crystals form fromMagma cooling andsettle to floor of chamber
Crystals from earlycooling accumulate
Weathering anderosion
Sedimentary rocks
Burial and lithificationinto sedimentary rock
Ocean transport anddeposition by currentsand chemical precipitation
Land transport and depositionby 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
Metamorphic rocks
SUMMARYMinerals
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.
SUMMARYThe 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.
SUMMARYHow 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
SUMMARYThe 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.
SUMMARYRocks
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.