CHAPTER 6 : CHAPTER 6 : LAND LAND AND ITS RESOURCESAND ITS RESOURCES

6.1 The Various Minerals 6.1 The Various Minerals Found in the Earth’s Crust.Found in the Earth’s Crust.

Mineral is natural element or compound found in the Earth’s crust.

has a composition and a specific crystalline structure.

Examples of minerals are calcite, feldspar, quartz, mica, marble and silicate.

Natural elements commonly found in the Earth’s crust are gold, silver, platinum, mercury and arsenic.

Elements in minerals found Elements in minerals found in thein theEarth’s crust.Earth’s crust.

MineralsMineralsAlmost 75% of the

weight of a mineral in the Earth’s Crust is made up of oxygen and silicon elements. Thus, silicate minerals which contain oxygen and silicon elements make up the largest amount. Examples of silicate minerals include quartz, feldspar, mica and clay.

Non-silicate mineralsNon-silicate mineralsMinerals that do

not contain silicon element are known as non-silicate minerals.

Examples of non silicate minerals are calcite, dolomite, magnetite and hematite.

Non-metallic elementsNon-metallic elements

Other non metallic elements such as oxygen, sulphur and carbon usually exist in the form of compounds such as oxides, sulphides and carbonates.

Elements in natural Elements in natural compoundscompounds

Oxygen combines with metal chemically form an oxides

Metal + oxygen Metal oxide

Eg : Iron oxide, copper oxide

Carbonates are compounds that contain oxygen, carbon and metals

Metal + oxygen + carbon Metal carbonate

Eg: sodium carbonate, zinc carbonate

Sulphur combines with metals, sulphides are formed

Metal + sulphur Metal sulphide

Eg : copper sulphide, silver sulphide

Metals combine with oxygen and silicon formed a silicates

Metal + oxygen + silicon Metal silicate

Eg : calcium silicate, and magnesium silicate

Properties of mineralsProperties of minerals

HardnessHardnessHardness of mineral refers to the resistance

offered by the mineral on being scratched. The hardness of a mineral is measured in Moths unit.

Most minerals are hard. These minerals can only be scratched by hard objects such as knives. Nevertheless, hard minerals can scratch softer minerals.

All minerals made up of carbonate, oxide and sulphide compounds are hard.

Diamond is the hardest mineral while talc is the softest mineral.

Reactivity and Solubility in Reactivity and Solubility in waterwaterReactivity and Solubility in Reactivity and Solubility in waterwaterNatural elements are non-reactive

elementsThese elements tend to remain as

elements without combining with any other substances

All minerals of metal oxides, sulphides and carbonates are insoluble in water, except minerals of metallic potassium and sodium compounds.

Reaction to heat and its Reaction to heat and its effects.effects.Reaction to heat and its Reaction to heat and its effects.effects.

i. Action of Heat on Metal Carbonates

All metal carbonates decompose when heated, except potassium carbonate and sodium carbonate because both the metal carbonates are very stable.

The heating of metal carbonates form metal oxides and carbon dioxide gas.

Metal carbonates metal oxide +

carbon dioxide

Eg : calcium carbonates

calcium oxide + carbon dioxide

Zinc carbonates

Metal carbonates metal oxide +

carbon dioxide

Eg : calcium carbonates

calcium oxide + carbon dioxide

Zinc carbonates

Carbon dioxide gas released Carbon dioxide gas released can be tested with:can be tested with:

i. Turn lime water milky

ii. extinguished burning splinter

iii. changes red bicarbonate indicator to yellow

Glowing splinter

ii. Action of Heat on Metal oxides

Most metal oxides are stable and do not decompose when heated.

Nevertheless, mercury oxide and argentums oxide are exceptions.

Both these metal oxides will decompose into oxygen gas and their original metal when heated.

Mercury oxides mercury + oxygen

Argentums oxides argentum + oxygen

*Oxygen gas released can be tested with;

i. the glowing splinter will burn brightly

Reaction to heat and its Reaction to heat and its effects.effects.Reaction to heat and its Reaction to heat and its effects.effects.

iii. Action of Heat on Metal Sulphides

Most metal sulphides will decompose when heated strongly to form metal oxides and produce sulphur dioxide gas.

Metal sulphides metal oxide +

sulphur dioxide

Eg : iron sulphides iron oxide +

sulphur dioxideZinc Sulphides

Reaction to heat and its Reaction to heat and its effects.effects.Reaction to heat and its Reaction to heat and its effects.effects.

Sulphur dioxide gas released is acidic, has a pungent smell and;

i. bleaches acidic purple potassium manganate (VII) colourless

ii. converts orange acidic potassium dichromate (VI) to green.

sulphur dioxide gas released sulphur dioxide gas released can be tested with:can be tested with: