UNIT  6  ROCKS

In geology, a rock is a naturally occurring solid aggregate of one or more minerals or mineraloids. The Earth's outer solid layer, the lithosphere, is made of rock.

Rocks are geologically classified according to characteristics such as mineral and chemical composition, permeability, the texture of the constituent particles, and particle size. These physical properties are the end result of the processes that formed the rocks. Over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock:

• igneous
• sedimentary
• metamorphic

 

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Sedimentary rocks are formed from sediment grains deposited by water, wind or ice. They are always formed in layers, called “beds” or “strata”, and quite often contain fossils.

 

Igneous rocks are formed from molten rock called magma. They are mostly crystalline (made up of interlocking crystals) and usually very hard to break.

Metamorphic rocks were once igneous or sedimentary rocks, but have been changed (metamorphosed) as a result of intense heat and/or pressure within the Earth’s crust. They are crystalline and often have a “squashed” (foliated or banded) texture.

 Let´s see a video about rocks:

 

 

And now, play a game about identifiying rocks (click on the picture):