Rocks, an Introduction

The climber is climbing a granite rock face

Rocks are all the same, aren’t they? Well, not quite. Much of the Earth’s crust is covered by water, sand, soil and ice. If you dig deep enough, you will always hit rocks. Sometimes, of course, they are on the surface and people climb them!

  • The Crust makes up less than 1% of the Earth’s mass (0.4%)
    It is made of oxygen, magnesium aluminum, silicon calcium, sodium potassium, iron.
    There are 8 elements that make up 99% of the Earth’s crust.
    The continents are about 35 km thick and the ocean floors are about 7-10 km thick, but the oceanic rock is denser.
  • The Mantle is the solid casing of the Earth and is about 2900 km thick.
    It makes up about 70% of the Earth’s mass (68.1%).
    It is made up of silicon, oxygen, aluminum and iron.
  • The Core is mainly made of iron and nickel and makes up about 30% of the Earth’s mass (31.5%).
    The Outer Core is 2200 km thick and is liquid and the Inner Core is 1270 km thick and is solid.

A rock is made up of 2 or more minerals.

Think of a chocolate chip cookie as a rock. The cookie is made of flour, butter, sugar & chocolate. The cookie is like a rock and the flour, butter, sugar & chocolate are like minerals.
You need minerals to make rocks, but you don’t need rocks to make minerals. All rocks are made of minerals. A mineral is composed of the same substance throughout. If you were to cut a mineral sample, it would look the same. throughout.
There are about 3000 different minerals in the world.
Minerals are made of chemicals we’ve seen or heard about before and are sorted into 8 groups.
Some common examples have been listed for each.

  • Native Elements~ copper, silver, gold, nickel-iron, graphite, diamond
  • Sulphides ~ sphalerite, chalcopyrite, galena, pyrite
  • Halides ~ halite, fluorite
  • Oxides& Hydroxides ~ corundum, hematite
  • Nitrates, Carbonates, Borates ~ calcite, dolomite, malachite
  • Sulphates, Chromates, Molybdates, Tungstates ~ celestite, barite, gypsum
  • Phosphates, Arsenates, Vanadates ~ apatite, turquoise
  • Silicates ~ quartz, almandine garnet, topaz, jadeite, talc, biotite mica

Some people make up stories and legends about rocks. These amethyst crystals in the picture are sometimes naturally hollowed out into ‘geodes’ where the ‘little people’ were supposed to live!

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