exer 1.2

• Soil horizon


  Layer of soil with distinct characteristics

  
• Soil structure


  • Granular
  • Blocky
  • Platy
  • Prismatic

  
• Recognized transitional horizons


  • AB
  • BA
  • AC
  • EB
  • BE
  • BC
• Subhorizon symbols


  • a
  • b
  • c
  • e
  • f
  • g
  • h
  • i
  • k
  • m
  • n
  • o
  • p
  • q
  • r
  • s
  • t
  • v
  • w
  • x
  • y
  • z
• Rock


  Aggregate of one or more minerals, most commonly two or more
• Classification of rock


  • Igneous
  • Sedimentary
  • Metamorphic
• Weathering


  The process whereby rocks are broken down and decomposed by physical, chemical and biological processes
• Types of weathering


  • Physical
  • Chemical
  • Biological
• Biological weathering


  • Animal burrows
  • Tree and plant roots
  • Lichens
• Mineral


  Grows by addition of atoms to crystal structure as matter changes from gaseous/liquid to solid state
• Mineral composition


  • Definite chemical composition with specific elements in definite proportions
  • Can vary within limits due to ionic substitution
• Cleavage


  Splitting of mineral along definite planes
• Types of cleavage


  • Perfect
  • Distinct
  • Indistinct
• Fracture


  Breaking of mineral regularly
• Cleavage


  Easy breakage of a mineral along a plane surface
• Cleavage


  • Mica
• Fracture


  The way a mineral breaks when it does not break along cleavage planes
• Types of fracture


  • Concoidal
  • Hackly: jagged and sharp
  • Fibrous and splintery
  • Uneven or irregular: rough & irregular surfaces
• Concoidal fracture


  • Quartz
  • Obsidian
• Streak


  The colored powder left when an opaque mineral is rubbed on a streak plate
• Luster


  How light is reflected from the surface of a mineral
• Types of luster


  • Metallic
  • Non-metallic: vitreous or glassy; silky; resinous; pearly; greasy; waxy, dull; earthy
• Hardness


  A measure of a mineral's resistance to abrasion
• Mohs hardness scale


  A relative scale of a mineral's resistance to scratching
• Crystal forms


  • Cube
  • Tetrahedron
  • Octahedron
  • Dodecahedron
  • Rhombohedron
  • Prismacoid
  • Pyritohedron
  • Dipyramids
• Rock-forming minerals


  • Feldspars
  • Micas
  • Quartz
  • Ferromagnesian minerals (biotite, olivine, pyroxenes, amphiboles)
  • Clay minerals
  • Calcite
  • Dolomite

  
• Feldspars


  Pink, porcelain-like mineral with rectangular shape and milky white, porcelain-like mineral that is somewhat smaller but similarly shaped. Have good cleavage in two directions, a porcelain-like luster, and a hardness of about 6 on Mohs' scale. Potassium feldspar (KAlSi3O8) and plagioclase feldspar (NaAlSi3O8 to CaAl2Si2O8)
• Micas


  • Perfectly one-directional cleavage, which permits the mineral to be broken easily into thin, elastic flakes. Complex silicate with a sheet structure that is responsible for its perfect cleavage. Two common varieties: biotite (black mica) and muscovite (white or colorless mica)
• Quartz


  • Lacks well-developed crystal faces, abundant in all three major rocks, simple composition SiO2, hardness of 7, concoidal fracture, and glassy luster. Forms elongated, six-sided crystals that terminate at a point
• Ferromagnesian minerals


  • Silicate minerals containing appreciable amounts of iron and magnesium. Generally dark green to black in color and have high specific gravity. Include biotite, olivine, pyroxenes, and amphiboles
• Olivine


  • Green glassy mineral with a composition of (Mg, Fe)2SiO4. Characterized by an olive green color (if Mg is abundant) and a glassy luster. Rarely forms crystals larger than a millimeter in diameter. A high-temperature mineral common in basalt
• Amphiboles


  • Composition similar to pyroxenes but contain hydroxyl ions (OH-). Have elongate crystals that cleave perfectly in two directions, not at right angles. Color ranges from green to black. Common in metamorphic rocks known as amphibolite. Hornblende is the most common variety
• Clay minerals


  • Constitute a major part of soil and common dirt. They are sheet silicates, but crystals are microscopic and usually can be detected only with an electron microscope. Distinguished by their crystal structures and variation in composition

  
• Calcite


  • Calcium carbonate, the principal mineral in limestone. Can be precipitated directly from seawater, removed from seawater by organisms and used to make their shells or dissolved by ground water and reprecipitated as new crystals. Hardness of 3 and effervesces in dilute hydrochloric acid. Has perfect cleavage in three directions but not at right angles, so cleaved fragments are in the form of rhombohedra
• Dolomite


  • Carbonate of calcium and magnesium. Large crystals form rhombohedra, but most dolomite forms granular masses of small crystals. Widespread in sedimentary rocks, having been altered from the original calcite through the activity of solutions of magnesium carbonate in seawater or ground water. Effervesces in dilute HCl only if in powder form