Student Library

Minerals

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Objectives

  • Define what is a mineral.
  • Identify the processes behind the formation of minerals.
  • Identify different properties used to identify minerals.
  • Classify different minerals according to their composition

What is a Mineral?

Mineral

  • It is a naturally-occurring, inorganic solid.
    • This means that it cannot be man-made or machine-generated.
    • They cannot be a product of living things (eg. coal, fossils)
    • This also indicates that they are solid at normal temperature ranges in Earth
  • It has orderly crystalline structure that also has a definite chemical composition.

Mineralogy

  • study of minerals, their properties, classification, crystallography and ways of distinction.

Formation of Minerals

  • Minerals form in one of four major processes:
    • Crystallization from Magma
      • As molten magma from the depths of the Earth cools, it can form minerals.
    • Precipitation
      • Substances that are dissolved in water may react to form minerals.
    • Pressure/Temperature Changes
      • Subtle changes in temperature and pressure can make new minerals form.
    • Crystallization from Hydrothermal Solutions
      • When some heated solutions touch minerals, chemical reactions may take place and form new minerals.

Properties of Minerals

  • Minerals have distinct properties.
  • These properties can be used to distinguish and identify different minerals
    • Luster:
      • It describes how light is reflected off the surface of a material.
      • It can be classified as metallic and non-metallic.
        • Metallic is described as generally opaque and shiny.
        • Non-metallic can be described as dull, glassy, resinous, silky, or greasy.
    • Color:
      • It describes the wavelength of light absorbed and reflected by the crystal.
      • They can be an unreliable diagnostic property.
        • Impurities within the mineral may give them a different color.
    • Streak:
      • It describes the color of the crystal when in powder form.
      • They can be a better diagnostic property than color.
    • Breakage
      • This determines how a mineral breaks.
      • They can be classified as cleavage and fracture.
        • Cleavage is the tendency to create flat surfaces when it breaks.
        • Fracture is when a mineral breaks unevenly, irregularly, and non-planar
    • Specific Gravity
      • It determines how heavy a mineral is.
      • It is often referred to its density.
    • Crystal Form/Crystal Habit
      • It determines the shape of the crystal as they grow.
      • It can also describe the layout or arrangement of the atoms inside the mineral.
      • Their crystal arrangement can be described as: isometric, tetragonal, orthorhombic, hexagonal, and triclinic
        • Isometric is a shape with each face is relatively similar and symmetrical
          • Examples are cubic, octahedron, dodecahedron.
          • Tetragonal is a shape characterized with a four sided pyramid and a rectangular prism.
          • Orthorhombic is a shape with a rectangular prism and a rectangular base.
          • Hexagonal has three symmetrical axes that occur in the same plane with the same length.
          • Triclinic has three axis where each has different lengths.
    • Hardness
      • It is a measure of the resistance of a mineral to being scratched.
      • We test hardness by scratching a mineral against an other material with a known hardness.
        • When one scratches the other, then it is harder than the other material
        • When they have the same hardness, then both of them scratches one another.
        • It is them measured using the Mohs’ Scale.
          • It is designed by Friedrich Mohs in 1812.
          • It consists of minerals arranged from softest to hardest.
            • This is where 1 is the softest and 10 is the hardest.
    • Other Properties
      • Some other unique properties can be used in its identification.
      • Some of them includes: magnetism, odor, taste, tenacity, reaction to acid, etc.

Types of Mineral according to Composition

  • Minerals can be grouped into two types: silicate and non-silicate minerals
    • Silicate Minerals
      • They are made of silicon and oxygen.
      • They are considered as the most common minerals on Earth.
        • 90% of rock-forming minerals belong to this type.
      • They usually form by crystallizing cooling magma.
    • Non-silicate Minerals
      • They are not made of silicon and oxygen.
      • They can be classified further into: carbonates, oxides, sulfates, sulfides, halides, and native elements.
        • Carbonates are minerals with carbon, oxygen and one or more other metallic elements
        • Oxides are minerals that contain oxygen plus one or more other elements that are usually metals.
        • Sulfates are minerals containing a sulfur and oxygen anion plus other ions.
        • Sulfides are minerals containing a sulfur anion plus one or more ions
          • They are also sources of some important metals, such as zinc, copper, or lead.
        • Halides are minerals containing a halogen ion plus one or more elements.
        • Native Elements are minerals composed of one type of element or atom.
          • Can be classified further into three types:
            • Metals and Inter-metals have high thermal and electrical conductivity, has metallic luster, and low hardness.
            • Semi-metals have lower conductivity and are more fragile than metals.
            • Non-metals are non conductive.

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