Untitled

• Mineral


  Naturally occurring chemical compound
• 90 of the known elements form mineral species, but most of the earth's crust is composed of only 11 elements
• Average Composition of the Earth's Crust

  • Oxygen (46.60%)
  • Silicon (27.72%)
  • Aluminium (8.36%)
  • Iron (5.00%)
  • Calcium (3.63%)
  • Sodium (2.83%)
  • Potassium (1.84%)
  • Magnesium (2.09%)
  • Titanium (0.44%)
  • Hydrogen (0.14%)
  • Phosphorous (0.12%)
• Only very tiny quantities of most economically important metallic elements are present in the average rock of the earth's crust
• Anion and cation size ratio

  • If approximately 1:2, six of the larger ions will pack in an octahedral structure with a space just the correct size for the smaller ion inside
  • If approximately 1:3 (as with silicon and oxygen), four of the larger ions can pack in a tetrahedral structure with a space just the correct size for the smaller ion to fit inside
• SiO4^4- complex ion


  Very stable covalent combination, forms the basis of a very important mineral group called Silicate minerals which compose over 95% of the earth's crust
• Chemical classification of minerals

  • Silicates
  • Carbonates
  • Sulphates
  • Phosphates
  • Oxides
  • Hydroxides
  • Halides
  • Sulphides
  • Native elements
• Almost all rocks are a combination of silicate minerals, and only under very special circumstances are rocks formed that containing less than 50% silicate minerals
• The silicate ion complex does not have an affinity for many of the economically important 'transition' group of metals, and silicates require high extraction energies, so almost all the metalliferous ore minerals belong to the non-silicate group
• Certain silicate and non-silicate minerals have economic importance as a result of their special physical and chemical properties, rather than their chemical composition, and are referred to as industrial minerals
• Colour


  • The most obvious but least reliable physical attribute of a mineral
• Lustre classifications- ability of a mineral to reflect light

  • Metallic
  • Vitreous (glassy)
  • Resinous (duller than glassy)
  • Pearly
  • Silky
  • Adamantine (sparkles like a diamond)
  • Opalescence and iridescence
• Transparenc

  The ability of a mineral to transmit light, classified as transparent, semitransparent, translucent and opaque
• Crystal systems


  • Cubic
  • Orthorhombic
  • Tetragonal
  • Hexagonal
  • Monoclinic
  • Triclinic

  
• Cleavage and fracture


  When broken, some minerals fracture with an uneven surface, but others split or cleave along distinctive crystallographic planes
• Mineral forms

  • Crystallised or euhedral (well developed crystals)
  • Crystalline (intergrown crystals)
  • Microcrystalline (microscopic crystals)
  • Cryptocrystalline (sub-microscopic crystals)
  • Irregular or anhedral (no evidence of the crystal structure)

  
• Mineral aggregate forms

  • Acicular (needle like)
  • Bladed
  • Stellate (star shaped)
  • Botriodal
  • Columnar
  • Dendritic (tree like)
  • Fibrous
  • Reniform (kidney shaped)
  • Wiry
• Texture


  Described as smooth, greasy, unctuous (soapy), and harsh or rough
• Topographic surface


  Hills and valleys are formed by erosion of geological layers of rock. The differences in hardness, thickness and orientation of the various layers result in the varieties of landforms that exist.

  
• Geological features that terminate on the hillside on one side of a valley continue on the other hillside
• Contour line


  A line on the map joining points of equal elevation

  
• Contour interval

  The difference in elevation between the contours

  
• Spacing of contour lines

  Indicates the steepness of the slope

  
• Map scale


  The ratio of the sizes of the map and the real surface

  
• If two maps of a particular area are drawn such that the one map is twice as big as the other, they will have different scales
• Cross section


  A side view of a vertical cut through the map area

  
• Constructing a cross section

  1. Choose section line

  2. Draw base line (X-axis) same length as section line

  3. Choose vertical scale (Y-axis)

  4. Transfer positions of contour lines crossing section line to X-axis

  5. Mark elevation of each contour on Y-axis

  
• If the vertical scale of the cross section is the same as the scale of the map, then the section is a true representation of the topography

  
• If the vertical scale is smaller, the section is exaggerated vertically making hills appear higher, valleys deeper, and slopes steeper than in reality

  
• Horizontal strata

  Undeformed sedimentary and volcanic layers of rock that form horizontal layers

  
• Lithological boundary/contact

  The boundary between each layer of rock

  
• The intersection of lithological strata and the topography result in a rock outcrop

  
• The highest layers in the sequence (youngest beds) will outcrop on the highest ground and the lowest (oldest) in the deepest valleys
• Inclined strata

  Strata that are referred to as dipping strata
• Dip angle

  The angle of inclination measured from the horizontal

  
• Strike

  The azimuthal orientation of a horizontal line drawn on the surface of the inclined layer

  
• The outcrop patterns of inclined strata are defined both by the topography and the inclination (dip angle and strike direction) of the layers

  
• Strike line


  Horizontal lines drawn on the inclined plane and projected onto the map surface

  
• Constructing strike lines


  1. Draw line through two points where outcrop pattern crosses contours of same elevation

  2. Direction of strike line indicates strike direction of layers

  
• If strike lines for different lithological contacts in a sequence of inclined layers are parallel and equidistant, the thickness of each layer is constant laterally and down dip