Upload
benedict-newman
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
Course aimsCourse aims
• Aims to understand: – the basic nature of the principal rock forming
minerals– Igneous, sedimentary and metamorphic rocks
• Provides:– the means of identifying & differentiating minerals
and rocks in hand specimen
• Practicals:– Provide experience of handing and describing
geological materials
Reading and AssessmentReading and Assessment
Reading:• Press, F. & Siever, R. 1994. Understanding Earth,
Freeman
Assessment:• Practical file (worth 20% overall, to include all
practicals)• Examination (80%), with pass mark of 40% overall.
Reading:• Press, F. & Siever, R. 1994. Understanding Earth,
Freeman
Assessment:• Practical file (worth 20% overall, to include all
practicals)• Examination (80%), with pass mark of 40% overall.
Course outlineCourse outline
Part 1: MineralsPart 1: Minerals• Session 1: Introduction to minerals & crystal structures • Session 2: Use of physical properties in the identification of
minerals in hand specimens• Session 3: Silicate minerals: their nature and general properties• Session 4: Non-silicate minerals their nature and general
properties
Part 2: RocksPart 2: Rocks• Session 5: Introduction to rocks and the rock cycle: igneous rocks• Session 6: Sedimentary rocks – Clastics• Session 7: Sedimentary rocks – Carbonates• Session 8: Metamorphic rocks – general characteristics USE IN
THE PRACTICALS
MINERALSMINERALS
•MineralsMinerals are naturally occurringnaturally occurring,, homogeneoushomogeneous,, crystalline solidcrystalline solid with a definite chemical definite chemical compositioncomposition
•Minerals usually form by inorganic processes but some may be biogenic in origin
Halite – NaClHalite – NaCl
Biotite – KBiotite – K22(Mg,Fe(Mg,Fe2+2+))44 (Fe (Fe3+3+,Al,),Al,)22(Si(Si66 Al Al22 O O2020))
(OH,F)(OH,F)44
Quartz:Quartz: primary rock forming mineral, simple silicate
Olivine:Olivine: primary rock forming mineral, complex silicate
Other Minerals:Other Minerals: PyritePyrite, an iron sulphide
Biogenic minerals:Biogenic minerals: Modern shell debris composed of carbonatecarbonate & silicasilica minerals
ROCKSROCKS
• A rock is:A rock is:• a naturally formed aggregate of mineral matter constituting a significant part of the Earth's crust.• Rocks can be consolidated or non-consolidated• Rocks can be monomineralic or an aggregate of mineral species• Rocks usually form by inorganic processes but some may be biogenic in origin
Granite:Granite: polished section showing aggregate of four interlocking and different coloured minerals
Concrete:Concrete: non-natural aggregate of other rocks set in a matrix
Cement matrix
Crushed rocks
Limestone - biogenic
Evaporite - inorganic
Biogenic and Biogenic and inorganic inorganic sedimentary rockssedimentary rocks
Coal - biogenic
Part 1: MineralsPart 1: Minerals
• A mineral is:A mineral is:
• A naturally occurring, crystalline solid with a definite chemical composition
• Structurally homogeneous– Atomic structure is continuous and
constant throughout the mineral structure– Mineral structure expressed as the Unit
Cell
The Unit CellThe Unit Cell
• Unit CellUnit Cell is the smallest 3D repeating unit of acrystal structure representative of its:• atomic structure• chemical composition• crystal symmetry
• Unit Cell is a regularly ordered arrangement of atoms with a fixed geometry relative to one another
• The atoms are arranged in a ‘box’ with parallel sides, the unit cell,unit cell, which is repeated by simple translations to make up the crystal
• Unit cell dimensions measured in angstroms with 1A = 10-10m
TEM image of Cordierite Cordierite (Mg2Al4Si5O18) showing ordered structure typical of
crystalline structures
20A
Macrocrystals of CordieriteCordierite showingwell developed flat crystal faces thatcharacterise crystals in their macroform
Micro Macro
Crystal Systems: common groups of symmetryCrystal Systems: common groups of symmetry
Crystal symmetry is defined Crystal symmetry is defined by:by:
• Planes of symmetry
• Axes of rotation
• Axes of inversion
All properties of a crystal substance conform to symmetry
Symmetry is the defining property of a crystal
Unit cell dimensions of the seven crystal systemsUnit cell dimensions of the seven crystal systems
• CUBIC a b c; αβγ• TETRAGONAL a b c; αβγ• ORTHORHOMBIC a b c; αβγ• MONOCLINIC a b c; αγβ• TRICLINIC a b c; αβγ• HEXAGONAL a b c; αβγ• TRIGONAL – Hexagonal
a b c; αβγ • TRIGONAL – Rhombohedral
a b c; αβγ
Where a, b, and c are the unit cell axes dimensions and α, β, and γ are the inclination angles of the axes in the unit cell.
The crystal systems can be defined by their stacked unit cellsThe crystal systems can be defined by their stacked unit cells
Crystal StructuresCrystal Structures
All crystal structures can be envisaged as:• the packing together of spherical ions/atomspacking together of spherical ions/atoms • bonded by ionicionic and/or covalentcovalent and/or metallicmetallic bonds
e.g. NaCl - Salt
Ionic bondIonic bond: • Electrical attraction between ions of opposite charge (Na+, Cl-)•90% minerals are ionic compoundsCovalent bond:Covalent bond:• shared electrons where electrons not readily lost/gained•E.g. DiamondMetallic bond:Metallic bond:• free-electron sharing in metallic atoms (loose electrons)
Crystal GrowthCrystal Growth
• Crystal growthCrystal growth can be envisaged as addition of unit cells in three dimensions
• If this occurs at the same ratesame rate in all directions the shape of the unit cell will be retained in the macro shape of the unit cell will be retained in the macro crystalscrystals
• If the rate of addition of unit cells is not the sameis not the same in all directions the shape of the macro crystals need not reflect the unit cell shape
• The symmetry of the macro crystals ALWAYSALWAYS reflects at least the minimum symmetry of the crystal system of the unit cell.
Calcite structure Calcite rhomb
CalciteCalcite
Unit cell Crystal
Calcite crystal habit
Ionic bond
Unit Cell ofpyrite
Pyrite crystals: ideal growth
Pyrite nodular aggregate:
confined growth
PyritePyrite
Unit cell