CHAPTER 6

LAND AND ITS RESOURCES

6.1 Minerals in the Earth’s Crust• Rocks are made up of minerals found in the Earth’s crust• Mineral: any solid element or compound that is found

naturally in the Earth’s crust• Examples of minerals: gold, limestone (calcium carbonate),

silver and etc.

• Minerals exist in the form of natural elements or natural compounds.

• Only a small amount of minerals exist in the earth’s crust as natural elements.

• Eg of natural elements: gold, silver, platinum• Most of the minerals exist in the form of

natural compounds• Eg: oxides, sulphides, carbonates and silicates

Natural compound Mineral Elements

Oxide Haematite Iron, oxygen

Cassiterite Tin, oxygen

Carbonate Calcite Calcium, oxygen. Oxygen

Malachite Copper, carbon, oxygen

Sulphide Iron pyrite Iron, sulphur

Galena Lead, sulphur

Silicate China clay Aluminium, silicon, oxygen

Calcium silicate Calcium, silicon, oxygen

Elements present in minerals that are found as natural compounds

Properties of minerals

• Each of the mineral has its own properties.• Different composition of minerals generally

possess the following properties:– Hardness– Solubility in water– Effect of heat

Hardness of minerals

• Generally, minerals are hard• All mineral oxides, sulphides and carbonates

are hard but the hardest mineral is the diamond

Solubility of minerals in water

• Most minerals are insoluble in water • Only oxides, sulphides and carbonates of

potassium and sodium are soluble in water.

Action of heat on minerals

• Most metal oxides are stable in high temperature.

• They do not break down when heated

• When heated, sulphides break down to metal oxides and sulphur dioxide is released.

Metal oxides

Metal sulphides

Metal sulphide metal oxide + sulphur dioxide heated

• When heated, carbonates break down to metal oxides and carbon dioxide is released.

• The carbon dioxide produced turns limewater cloudy.

Metal carbonate metal oxide + carbon dioxide heated

Metal carbonates