Rocks and Minerals



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Chapter 8 : Rocks and Minerals



Rocks arrow_upward


  • A rock is defined as a solid mass that is naturally occurring and consisting of one or more minerals.
  • Rocks can be hard or soft, as small as a grain or as large as a building
  • Rocks are generally made up of two or more minerals, but minerals are not made of rocks.
  • Earth’s crust and part of its covering are made of rock.
  • Rocks have property of hardness, color, and texture.

  • Type of Rocks arrow_upward


  • Rocks are divided in different categories based on their origination.
    • Igneous Rocks
    • Sedimentary Rocks
    • Metamorphic Rocks
  • Rocks formed in different environments have different characters
  • Sand is also a type of rock.

  • Igneous Rocks arrow_upward


  • Igneous Rocks are formed from cooling and crystallization of molten rock- magma.
    • Magma- It is molten rocks within the Earth’s Surface.
  • Igneous Rocks make the outer layer of earth.
  • Igneous Rocks are formed when molten rock cools and solidify.

  • How are Igneous Rocks formed arrow_upward


  • Most important content of igneous rocks is Magma which is inside the earth crust.
  • Characteristics of Magma:
    • Igneous rocks are made of magma.
    • Form from particles melting from rocks.
    • Magma at surface is called lava.
  • Rocks formed from lava are extrusive, and generally called as volcanic rocks.

  • Sedimentary Rocks arrow_upward


  • Sedimentary rocks are formed by decomposition of material at Earth surface and within water bodies.
  • Due to action of wind, water, gravity, thermal expansion, rocks are divided into small pieces of rocks that are called Sedimentary Rocks.
  • Particles that form a sedimentary rock by accumulating are called sediment.

  • Types of Sedimentary Rocks arrow_upward


  • Clastic: This is made up of broken up particles.
  • Chemical/Biochemical:  These types of sedimentary rocks are formed by decomposition of organic material.

  • How are Sedimentary Rocks formed arrow_upward


  • Weathering breaks down rocks into finer material that further decompose as sediments.
  • The process of compaction and cementation of these sediments over long period of time turn sediments into rocks, these are sedimentary rocks

  • Metamorphic Rocks arrow_upward


  • Metamorphic rocks are those which change themselves under high pressure and temperature.
  • Metamorphic is derived from word metamorphism which means the process of “change in forms”.
  • Changes in these rocks occurred due to chemical reaction between minerals in the rock.
  • The chemical reaction is entirely in its solid state as in igneous rocks (changes occur in its molten state).

  • How are Metamorphic Rocks formed arrow_upward


  • These rocks are created by high pressure and heat and by some chemical reactions.
  • Metamorphic rocks are formed by other rocks through metamorphism process.
  • Metamorphism Process
    • It starts from low grade to high grade.
    • During this process rock remain essentially strong.
    • New material from preexisting minerals formed through recrystallization.
    • Deformation of existing minerals, change in shape and internal property.

    Weathering arrow_upward


  • Weathering is a process of breaking down rocks.
  • It is disintegration, or breakdown of rock material.
  • It allows new rocks to be formed over millions of years and then they emerge from the sea.
  • Soil also gains its fertility due to weathering.

  • Types of Weathering arrow_upward


  • There are basically two types of weathering:
    • Mechanical Weathering
    • Chemical Weathering

    Mechanical Weathering

  • In Mechanical weathering rocks break physically into small pieces.

  • Chemical Weathering

  • In this process rocks break atom by atom, water plays the most important role in chemical weathering.

  • The Rock cycle arrow_upward


  • Rock cycle is a group of changes in different types of rocks.
  • Igneous rock changes into sedimentary or metamorphic rock.
  • Sedimentary rock can change into metamorphic rock or into igneous rock.
  • Likewise metamorphic rock can change into igneous or sedimentary rock.
  • Igneous rocks are made of molten lava and when it cools down we get our rock
  • Through wind, small particles of sediments move from one place to another, which forms earth layers that make sedimentary rocks and likewise the cycle continuous.

  • Minerals arrow_upward


  • A mineral is a naturally occurring substance that is solid and stable at room temperature
  • It is representable by a chemical formula, usually a biogenic, and has an ordered atomic structure
  • The earth is made up of rocks, which are in turn made of minerals.
  • Minerals are the “building blocks” of rocks.
  • Five basic properties of minerals are as follow:
    • Occurs naturally
    • Not previously living (inorganic)
    • Solid
    • Definite chemical composition
    • Orderly internal atomic arrangement
  • Minerals are classified on the basis of:
    • Chemical composition (what elements they are composed of)
    • Crystal structure (how the elements are arranged)
  • Minerals are made of different ions bonded together.
  • Ions are charged particles
    • Cations are positively charged.
    • Anions are negatively charged.
  • Geologists determine the identity of an unknown mineral by describing its physical properties.
  • Every mineral have their own unique set of physical properties and characteristics.

  • Properties of Mineral arrow_upward


  • Luster- Refers to the light reflected off of the mineral.
  • Minerals can be termed: glassy, opaque, transparent, shiny.
  • One of the first determinations a geologist must make is whether the mineral in metallic or non-metallic.
  • Habitat- Distinctive shape of the way the mineral commonly (habitually) appears.
  • Minerals vary greatly in color and thus color is unreliable as a physical property in many minerals, e.g. quartz
  • Hardness - The ability to resist abrasion or scratching.
  • Crystal structure -Crystal structure depends on sizes of and charges on ions.

  • Type of Minerals arrow_upward


  • Metallic minerals: Minerals like gold, iron, copper are metallic they have all the properties of metal.
  • Metals: They are good conductors of heat and electricity, hard, lustrous, high melting and boiling point, etc.
  • All these properties are satisfied by metallic minerals.
  • Non Metallic minerals: Minerals like Quartz and Diamond are nonmetallic they have all the properties of nonmetals.
  • Nonmetals: They are not good conductors of heat and electricity and do not possess very high melting and boiling point.
  • These properties are for all nonmetallic minerals.

  • Some information about Minerals arrow_upward


  • Minerals are found in the form of ores beneath the earth.
  • The ores must be processed to extract the metals of interest from the waste rock and from the ore minerals.
  • Commercially valuable minerals and rocks are referred to as industrial minerals.
  • Our food contains minerals, which is necessary for our body to be fit.
  • The most common mineral that is used in our food regularly is salt (NaCl).
  • The study of minerals is called mineralogy.
  • A mineral is sometimes made up of just one chemical element but more often it is a compound (mixture) of two or more.
  • For example, diamonds are made up of just carbon, while fluorite is made up of a compound of calcium and fluorine.


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