O Level Environmental Management: Rocks and Minerals — Revision Notes

Condensed for the final weeks. For the full explanation, use the Rocks and Minerals study guide.

Rock types

Type	Formation	Examples
Igneous	Cooling and solidification of magma or lava	Granite (intrusive, slow cooling, large crystals), basalt (extrusive, fast cooling, small crystals)
Sedimentary	Compaction and cementation of sediments	Limestone, sandstone, shale
Metamorphic	Existing rock altered by heat and/or pressure	Marble (from limestone), slate (from shale)

Crystal size in igneous rock indicates cooling rate — slow cooling underground allows large crystals to grow, rapid cooling at the surface does not. That link is the standard question, and it is a reasoning point rather than a fact to memorise.

Sedimentary rocks may contain fossils; igneous and metamorphic rocks do not, because the heat involved would destroy them.

The rock cycle

weathering and erosion -> transport -> deposition -> compaction (sedimentary)
   -> heat and pressure -> metamorphic
   -> melting -> magma -> cooling -> igneous
   -> uplift and exposure -> weathering again

The cycle is continuous and driven by two energy sources: internal heat from the Earth (for melting, uplift and metamorphism) and solar energy driving the water cycle (for weathering, erosion and transport).

Minerals and reserves

A mineral is a substance obtained by mining. A reserve is a known deposit not yet mined that could be extracted in future — reserve figures are estimates that change, rising as new deposits are discovered or higher prices make lower-grade ore viable, falling as extraction proceeds. A resource only becomes a reserve when extraction is economically viable.

Worked example. A country reports iron ore reserves of 400 million tonnes and extracts 8 million tonnes a year. Explain why “reserves will last 50 years” is unreliable.

400 / 8 = 50 years, but this assumes:
  - extraction rate stays constant (demand usually grows)
  - no new deposits are discovered (exploration continues)
  - the economic threshold is fixed (higher prices make low-grade ore viable)
  - no substitution or recycling reduces demand

The calculation itself is worth one mark; the reasons it is unreliable are worth the rest.

Extraction methods

Open-cast (surface) mining — cheap, safe, high recovery, but destroys a large surface area, creates dust and noise, and leaves visible scars.

Adit mining — a near-horizontal passage driven into a hillside to reach a seam, limited to deposits exposed on a slope.

Deep (shaft) mining — less surface damage, accesses deeper deposits, but is expensive, dangerous, and risks subsidence.

Choice depends on the depth of the deposit and its value — a shallow deposit is always cheaper to work by open-cast; deep mining is only justified where the ore is valuable enough.

Environmental impacts

• Land — habitat destruction, loss of farmland, spoil heaps, subsidence.
• Water — acid mine drainage, sediment in rivers, chemical contamination from processing.
• Air — dust, and emissions from machinery and smelting.
• Social — displacement of communities, noise, health effects, heavy traffic.

Balance the impacts against the benefits — employment, income and foreign exchange, raw materials for industry, and infrastructure development. Questions almost always ask for both sides plus a judgement.

Sustainable management

Reduce, reuse, recycle. Recycling metals uses far less energy than extracting from ore — aluminium recycling saves around 95% — and conserves the ore reserve.

Restoration after extraction: replace topsoil, replant native vegetation, landscape spoil heaps, and convert worked-out sites to lakes, nature reserves or recreational land.

Legislation and monitoring: environmental impact assessments before permission is granted, emission limits, restoration bonds requiring companies to fund site recovery, and monitoring during operation.

Sustainable use means meeting present needs without preventing future generations from meeting theirs. For a finite resource this means extending its life through efficiency, recycling and substitution rather than pretending it can be renewed.

Exam traps

• Confusing intrusive with extrusive igneous rock.
• Saying metamorphic rocks contain fossils.
• Describing extraction impacts without any benefits.
• Giving a management strategy without saying how it works.
• Not answering the question actually set in an evaluation.
• Vague answers with no named examples.

Self-test

1. What does crystal size in an igneous rock indicate, and why?
2. Why do metamorphic rocks not contain fossils?
3. Give one advantage and one disadvantage of open-cast mining.
4. Give three environmental impacts of mineral extraction.
5. What does sustainable use of a finite mineral resource mean in practice?
6. A country has 400 million tonnes of iron ore reserves and extracts 8 million tonnes a year. Give the simple calculation and explain why it is unreliable.
7. Distinguish between a mineral and a reserve.

Answers: 1. The rate of cooling — slow cooling underground allows large crystals to grow, whereas rapid cooling at the surface produces small ones. 2. The heat and pressure that form them destroy any fossils present in the original rock. 3. It is cheaper and safer with high recovery rates, but it destroys a large surface area and creates dust and noise. 4. Habitat destruction and loss of land; water contamination through acid mine drainage and sediment; air pollution from dust and machinery emissions. 5. Extending the resource’s life through efficient extraction, recycling and substitution, and restoring sites afterwards — since the resource itself cannot be renewed. 6. 400 ÷ 8 = 50 years, but this assumes a constant extraction rate, no new discoveries, a fixed economic threshold, and no substitution or recycling — all of which typically change. 7. A mineral is a substance obtained by mining; a reserve is a known deposit not yet mined that could be extracted in future, and only counts once extraction is economically viable.