Minerals and ores
Stones, coal, salt and the raw material of iron things from mines are part of our daily use.
Natural substances in the earth's crust are minerals (खनिजे). A mineral rich in a metal, from which the metal can be taken out economically, is an ore (धातुक).
Rule 1: Minerals form in four ways — (1) Magma cools and forms crystals. (2) Evaporation of a solution leaves crystals behind. (3) Heat and pressure change one mineral into another. (4) Some living things make mineral shells.
- Easy : When sea water dries up, salt crystals are left.
- Medium : A shell is a mineral made by a living thing for protection.
- Exam-type : When the magma of a volcano cools, crystals of minerals form in it.
Rule 2: Not every mineral is an ore — Only a few metals such as gold, silver, copper, platinum and bismuth occur free. Most metals occur as compounds. The sand and soil mixed in an ore is called gangue. Getting a metal needs extraction and purification.
- Easy : Gold is usually found in the free state.
- Medium : Iron is not found free; it must be extracted from its ore.
- Exam-type : If a mineral has very little metal, taking it out is too costly; it is a mineral but not an ore.
Mineral groups: non-metal minerals, metal minerals, energy minerals and gems.
Thinking every mineral is an ore. Only minerals rich in a metal and economical to use are ores.
Memory clue : "All ores are minerals, not all minerals are ores" — just as every square is a rectangle but not every rectangle is a square.
Spot the difference
| Group | Examples |
|---|---|
| Non-metal minerals | Mica, sulphur, gypsum, graphite |
| Metal minerals | Iron, gold, silver, bauxite |
| Energy minerals | Coal, mineral oil, natural gas |
| Gems | Diamond, ruby, emerald, sapphire |
Practice questions
- 1What is a mineral?
- 2What is an ore?
- 3Name two metals found in the free state.
- 4What is gangue?
- 5In which four ways do minerals form?
- 6In which group does mineral oil fall?
- 7Why are all minerals not ores?
- 8Name the two stages of obtaining a metal from its ore.
Show answers (try them yourself first)
- 1A natural substance in the earth's crust.
- 2A mineral rich in a metal that is economical to use.
- 3Gold and silver.
- 4The sand and soil impurities in an ore.
- 5By cooling of magma, evaporation, change by heat and pressure, and by living things.
- 6Energy minerals.
- 7Some have too little metal; extracting it is not economical.
- 8Extraction and purification.
Important minerals and their uses
Rails, electric wires, aeroplanes and kitchen utensils are made from different metals.
Every mineral has its own properties, and its use depends on them: iron is strong, copper conducts electricity and mica does not.
Rule 1: Use follows property — Iron ore gives everything from pins to heavy machines. Bauxite is the main ore of aluminium and has about 55% aluminium. Aluminium is light and conducts heat and electricity well. Copper is an excellent conductor. Mica does not conduct electricity.
- Easy : Copper wires carry electric current.
- Medium : Aluminium is light, so it is used in aeroplanes and vehicles.
- Exam-type : If 200 kg of bauxite has about 55% aluminium, that is about 110 kg.
Rule 2: Ores of iron and manganese — The four main ores of iron are magnetite, haematite, limonite and siderite. Manganese compounds are used in medicines, to give glass a pink tinge and in electrical appliances.
- Easy : Farm tools and rails are made from iron.
- Medium : Manganese compounds give glass a pink tinge.
- Exam-type : Because mica does not conduct electricity it is used in electrical machines as an insulating part.
The value of mica depends on the thickness of its layers.
Thinking mica conducts electricity. It does not.
Memory clue : "Iron = strong, Copper = wire, Bauxite = light, Mica = insulator" — learn each mineral with its quality.
Spot the difference
| Mineral | Key quality | Use |
|---|---|---|
| Iron | Strong | Rails, tools, machines |
| Bauxite | Gives light aluminium | Aeroplanes, wires |
| Copper | Excellent conductor | Wires, radios, utensils |
| Mica | Does not conduct | Electrical machines, dyes |
Practice questions
- 1Name two ores of iron.
- 2What is the main ore of aluminium?
- 3Which metal is an excellent conductor of electricity?
- 4Why is aluminium used in aeroplanes?
- 5Name a use of mica.
- 6What gives glass a pink tinge?
- 7How much aluminium is in 100 kg of bauxite with about 55% aluminium?
- 8Distinguish mica from copper with respect to electricity.
Show answers (try them yourself first)
- 1Magnetite and haematite.
- 2Bauxite.
- 3Copper.
- 4It is light.
- 5Electrical machines, dyes, ayurvedic medicines.
- 6Compounds of manganese.
- 7About 55 kg.
- 8Copper conducts electricity; mica does not.
Fuels: coal, mineral oil and natural gas
Cooking gas, petrol in vehicles and coal in power plants are fuels that give energy.
A substance burnt to get energy is a fuel (इंधन). Coal, mineral oil and natural gas are fossil fuels (जीवाश्म इंधने) because they formed from the remains of living things millions of years ago.
Rule 1: Coal — Buried plants are covered by soil; pressure from above and heat from the earth slowly turn them into coal. Types: peat, lignite, bituminous coal and anthracite. Anthracite is the best grade.
- Easy : Coal is burnt in thermal power plants.
- Medium : Producer gas and water gas are gaseous fuels obtained from coal.
- Exam-type : Of peat, lignite, bituminous coal and anthracite, anthracite is the highest grade.
Rule 2: Mineral oil and natural gas — Dead sea creatures are covered by soil and sand, and pressure and temperature turn them into mineral oil. It is taken out through oil wells and separated by fractional distillation into petrol, diesel, kerosene, tar and more. The main part of natural gas is methane (CH₄); it can be moved as CNG and LNG.
- Easy : Petrol and diesel come from mineral oil.
- Medium : CNG leaves no solid waste and produces no other pollutants.
- Exam-type : Where there is no pipeline, natural gas is moved as CNG or LNG under pressure.
Rule 3: LPG and the energy crisis — LPG has propane and butane in the ratio 30 : 70. Under pressure its volume shrinks to 1/240. A strong-smelling chemical, ethyl mercaptan, is added to detect leaks. Population grows while reserves are limited, so an energy crisis may come; alternatives are hydrogen, biofuels, methanol and ethanol.
- Easy : LPG is a liquid in the cylinder.
- Medium : LPG has no smell; a smell is added so leaks can be detected.
- Exam-type : When 240 litres of gas is liquefied under pressure it takes only 1 litre of space.
Fossil fuel reserves are limited; wasting fuel must be avoided.
Thinking oil and coal will never run out. They take millions of years to form.
Memory clue : "Coal = black gold, oil = liquid gold" — precious but exhaustible.
Spot the difference
| Fuel | State | Main part |
|---|---|---|
| Coal | Solid | Carbon |
| Mineral oil | Liquid | Mixture of hydrocarbons |
| Natural gas | Gas | Methane |
| LPG | Gas (liquid under pressure) | Propane and butane |
Practice questions
- 1What is a fossil fuel?
- 2Name four types of coal.
- 3What is the main part of natural gas?
- 4How is mineral oil separated into its parts?
- 5Why is a smell added to LPG?
- 6Give two advantages of CNG.
- 7What is an energy crisis?
- 8Name alternative fuels to fossil fuels.
Show answers (try them yourself first)
- 1A fuel formed from the remains of ancient living things.
- 2Peat, lignite, bituminous coal, anthracite.
- 3Methane.
- 4By fractional distillation.
- 5So that a leak is noticed at once.
- 6No solid waste; fewer pollutants.
- 7The possibility that fuel reserves may get exhausted.
- 8Hydrogen, biofuels, methanol and ethanol.
Forest resources
Timber for furniture, medicinal plants, honey and gum come from forests, and forests reduce floods and soil erosion.
A large area of land covered with many kinds of plants is a forest (जंगल). It is the natural home of plants, animals and microbes. About 30% of the world's land is covered by forests.
Rule 1: Protective functions — A forest slows the water flowing over land, prevents soil erosion, helps water seep into the ground, controls floods, reduces evaporation, protects wildlife and balances atmospheric gases.
- Easy : Roots hold the soil in place.
- Medium : On a forested hill rain water flows down slowly, so floods are reduced.
- Exam-type : If a forest is cut, less water seeps in and erosion increases.
Rule 2: Productive functions and conservation — Forests give timber (teak, eucalyptus, babul), fibre, paper, rubber, gum, fragrant oils (lemon grass, vetiver), fruits, tubers, honey, dyes and medicinal plants. To conserve them, do not cut young trees, plant and care for more trees than are cut, and follow forest laws.
- Easy : The cinchona tree gives a malaria medicine.
- Medium : Neem is used for fever and cold.
- Exam-type : If rubber ran out we would lose tyres, footwear and many other things; so forests must be protected.
Forests improve and maintain the quality of the environment.
Thinking a forest is only a store of timber. Its protective functions are equally important.
Memory clue : "Protective = erosion, floods, animals; Productive = timber, medicine, gum" — remember the two groups.
Spot the difference
| Type | Examples |
|---|---|
| Protective | Stopping erosion, flood control, protecting wildlife |
| Productive | Timber, paper, rubber, gum, medicines |
Practice questions
- 1About what percentage of the world's land has forests?
- 2Name two things we get from forests.
- 3Which tree gives a medicine for malaria?
- 4Give two protective functions of forests.
- 5Name two plants that give fragrant oil.
- 6Suggest two ways to conserve forests.
- 7What are the bad effects of destroying forests?
- 8How do forests reduce floods?
Show answers (try them yourself first)
- 1About 30%.
- 2Timber and honey (or gum, rubber).
- 3Cinchona.
- 4Preventing soil erosion and controlling floods.
- 5Lemon grass and vetiver.
- 6Do not cut young trees; plant more trees.
- 7Erosion, floods, loss of wildlife and an unbalanced environment.
- 8They slow the water and help it seep into the ground.
Ocean resources
Fish, salt, shells, pearls and oil drilled from the sea come from marine wealth.
Resources obtained from seas and oceans are marine resources (सागरी संसाधने). They include minerals, bio-resources and energy (waves, tides, currents).
Rule 1: Minerals and bio-resources — Sea water and the sea floor hold tin, chromium, copper, zinc, iron, sulphur, uranium and more. Oil and gas are found under the sea bed. Pomfret, seer fish and prawns give proteins and vitamins; shells go into medicines and ornaments; shark and cod oil gives vitamins A, D, E; fungi give antibiotics.
- Easy : Fish and prawns are eaten as sea food.
- Medium : Pearls and conches come from the sea; real pearls can cost more than gold.
- Exam-type : In India the drill-ship "Sagar Samrat" drilled an oil well at Bombay High in 1974.
Rule 2: Marine occupations and restraint — Fishing, salt farming, sea transport, sea tourism and making decorative articles are marine occupations. As resources are limited, avoid over-use to keep nature in balance.
- Easy : Salt farming is a big marine industry.
- Medium : Sea tourism brings income.
- Exam-type : Over-fishing can exhaust fish stocks; so use must be controlled.
Energy can be produced from waves, tides and ocean currents.
Thinking the sea has only fish and salt. It also has minerals, oil, gas and medicinal materials.
Memory clue : "Ocean = minerals + life + energy" — remember the three groups.
Spot the difference
| Group | Examples |
|---|---|
| Minerals | Tin, copper, sulphur, oil, gas |
| Bio-resources | Fish, prawns, conches, shells, fungi |
| Energy | Waves, tides, currents |
Practice questions
- 1What are marine resources?
- 2Name two minerals obtained from the ocean.
- 3Which drill-ship drilled the Bombay High well?
- 4Name two sea creatures used as food.
- 5How is energy obtained from the sea?
- 6Name four marine occupations.
- 7What is obtained from shark and cod fish?
- 8Why should marine resources not be over-used?
Show answers (try them yourself first)
- 1Resources obtained from seas and oceans.
- 2Tin and copper.
- 3Sagar Samrat.
- 4Pomfret and prawns.
- 5From waves, tides and currents.
- 6Fishing, salt farming, sea transport, sea tourism.
- 7Edible oil rich in vitamins A, D and E.
- 8They are limited; over-use will exhaust them.