Rocks are made of one or more minerals.
A mineral is a naturally occurring solid substance with its own chemical composition, structure and properties.
There are over 4,000 minerals in the world.
Quarts is the most common mineral in the world. Its made up of oxygen and silicon. Two of the most common elements on earth.
Minerals are formed in shapes called crystals.
The structure of the crystal greatly influences a mineral's properties.
Diamond and graphite have the same chemical composition, but graphite is soft while diamond is extremely hard.
In graphite the carbon atoms are arranged in sheets, while in a diamond they form an interlocking unit.
Identifying minerals
Geologist carefully examine the properties of rocks to determine what type of mineral they are. Unfortunately, the main colour of the mineral isn’t enough to judge the type of mineral. This is because many minerals are impure.
The animation to the right shows the difference between pure quartz and quart with various imperfections.
We can identify different types of minerals by their physical features.
Lustre
This means how shiny the rock is. Sometime it may look
Metallic (shiny new coin), brilliant (like a mirror), Pearly (like a pearl), dull (not shiny) or earth (lump of dirt).
Streak
When minerals are crushed, they form a powder. This powder has a colour. Often the streak is different from the main colour of the mineral
Hardness
How easily something can be scratched. Some minerals an be scratched with a fingernail, while other are incredibly tough. We can describe the hardness of minerals by using a 1 to 10 scale invented by Australian geologist Friedrich Mohs.
1 is the softest mineral like talc, while 10 is the hardest like diamond.
Cleavage
The number of smooth planes that minerals break along.
Calcite has three cleavages because it breaks with three smooth surfaces: left and right; front and back; top and bottom.
Here is a good website for rock identification
http://www.mineralogy4kids.org/mineral-
