4.2 How Minerals Form


solution: a mixture in which one substance dissolves in another
vein: a narrow channel or slab of a mineral that is much different from the surrounding rock


Processes that form minerals

  • The minerals that we use today were once deep underground in the earth for billion's of years
    • minerals can form in 2 ways; through crystallization of melted materials, and crystallization of materials melted in water
      • crystallization is the process by which the atoms are arranged to make a material with a crystal structure
Minerals from magma

  • When hot magma cools inside the crust and on the cool surface, minerals form
    • When the magma cools and turns to a solid, minerals form
      • The size of the crystals depend on how long it takes for the magma to cool, how much gas is in the magma, and the chemical composition of the magma
        • if the magma cools deep below the surface it cools slowly over thousands of years; and that means that there will be bigger crystals because slow cooling means bigger crystals
          • magma that is cooler to the surface cools faster and leads to smaller crystals
Minerals from hot water solutions

  • Sometimes the elements that form a mineral dissolve in hot water
    • these dissolved materials make up something called a solution
      • When a hot water solution starts to cool, the elements and compounds leave the solution and start to crystallize as minerals
      • pure metals that crystallize underground often form veins
        • Many minerals form from solutions at places where tectonic plates spread apart along the mid-ocean ridge

Minerals formed by evaporation

  • Minerals can also form when solutions evaporate
    • thick deposits of the mineral halite (table salt) formed over thousands of years when the ancient seas slowly evaporated
      • In the US, most halite deposits occur in the Midwest, the southwest, and along the Gulf coast
        • several other useful minerals form from the evaporation of sea water like gypsum which is used to make buildings, calcite crystals which is used in microscopes, and minerals containing potassium used in making fertilizer
Where minerals are found

  • the earth's crust is mostly made up of the common rock-forming minerals combined in different types of rocks
    • many valuable minerals are not distributed evenly throughout the world
      • lots of valuable minerals like gold and copper are found near areas of volcanic activity and mountain building like for example in the 1800s, California's rich gold deposits were found along the Sierra Nevada mountains

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