4.1 Properties of Minerals


Vocabulary


inorganic: Not formed of living things or from the remains of living things
crystal: A solid in which the atoms are arranged in a pattern that repeats again and again
element: A substance composed of a single kind of atom
compound: A substance in which two or more elements are chemically joined
Mohs hardness scale: A scale ranking ten minerals from softest to hardest; used in testing the hardness of minerals
streak: The color of a mineral's powder
luster: The way a mineral reflects light from its surface
cleavage: A mineral's ability to split easily along flat surfaces
fracture: The way a mineral likes like when it breaks apart in an irregular way
fluorescence: The property of a mineral in which the mineral glows under ultraviolet light

Outline


What is a Mineral?

    • geologist have already identified over 3,000 mineral
      • only 100 minerals are common
      • about 20 mineral make up earths surface
    • a mineral is an inorganic solid
      • a mineral always has a crystal structure
  • Naturally Occurring
    • minerals are not man made
  • Inorganic
    • mineral aren't made up of living things
      • since coal is made up of living things it is not a mineral
  • Solid
    • mineral must be solid
      • the particles must be packed together tightly
      • water is not a mineral since it is not solid
  • Crystal Structure
    • minerals need to have a crystal structure
    • crystal structures can sometimes be easy to identify but sometimes you can only identify it through a microscope
  • Definite Chemical Composition
    • a mineral always has certain elements in definite amounts
    • most minerals are compounds
      • a compound is a mineral that is made up of two or more elements combinedHardness_Scale_3.jpg

Identifying Minerals

    • in 1849, thousands of people went to California to find gold
    • few found gold, but many found minerals that look like gold
  • Hardness
    • to identify a mineral, finding the mineral's hardness is very useful
      • in 1812, Friedrich Mohs made the Mohs hardness scale
        • it ranks then minerals from softest to hardest
  • Color
    • it is easy to see what a mineral's color is
    • but a certain type of mineral can form in many different colors
  • Streak
    • the streak is the color of the mineral's powder
    • the color of the streak always stays the same color
  • Luster
    • minerals that look shiny is usually because they have metals inside them
      • Galena contains led and has a metallic luster
      • Malachite contains copper so it has a silky luster
  • Density
    • every mineral has its own density
    • the size doesn't change anything, its density will always stay the same
    • to compare the density you can lift 2 minerals that are the same size, one will probably weigh heavier
    • geologist measure the density of minerals by...
      • using a balance
      • place mineral in water to see how much water it displaces
      • dividing the mineral's mass by it volume
  • Crystal Systems
    • crystal structures are what kind of structure the atoms of the minerals grow into
    • there are six different structures so geologists seperate them into six different groups
    • crystals that grow in tight spaces are usually incomplete
    • crystal that grow in open spaces are almost perfectly complete
  • Cleavage and Fracture
    • identifying how a mineral breaks can help figure out what kind of mineral it is
    • a mineral that can break easily along flat surfaces have cleavage
      • have cleavage matters how the atoms in the mineral are arranged
        • if it is formed in a certain way, it'll be easier to break on one side than the other
    • most minerals don't split perfectly, this means the mineral is fractured
      • soft minerals have an earthy fracture
        • such as clay
      • rough minerals have an uneven fracture
  • Special Properties
    • minerals that glow under ultra-violet light have fluorescence
      • scheelite is fluorescent
    • some minerals contain magnetism
      • the mineral lodestone contains magnetism
    • a few minerals are radioactive
      • Uraninite can set off a Geiger counter
    • some minerals react chemically to acid
      • calcite will give off carbon dioxide if it touches vinegar
    • even some minerals have electrical properties
      • quartz has electrical properties

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