Rocks (P)

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TYPES OF ROCK

There are three main types of rock. These are sedimentarymetamorphic, and igneous.

Sedimentary rocks are formed by the accumulation of sand, shells, pebbles and other material.  All these are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock.

Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks.

Igneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (in this case, it is called lava).


State two characteristics each of the following rock types:

Sedimentary rocks. Igneous rocks.

Sedimentary rocks:

  1. Sedimentary rock is fairly soft and may crumble easily.
  2. Sometimes it contains fossil.

Igneous rocks:

  1. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.
  2. Some types of igneous rock look shiny and glasslike.

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