Rocks are classified into three main groups depending on how they are formed: igneous, sedimentary and

metamorphic.

Igneous rocks
When molten rock from the Earth’s crust or the upper mantle cools, it becomes igneous rock. If the molten rock is
still below the surface, it is called magma, but once it reaches the Earth’s surface, it is known as lava.

The mantle contains magma, which is hot liquid rock. Because of the weight of rocks above, this magma is kept
under pressure. Once it cools, it hardens into solid rock. If magma rises from a volcano and flows onto the surface, it
cools and turns into lava.

Igneous rocks come from rock that was once molten. As the molten rock cools, crystals usually develop inside it.
These crystals often contain valuable minerals, which are very important in many kinds of industrial processes.

Sedimentary rocks are formed in several ways: through the weathering of existing rocks at Earth’s surface, by the
precipitation of dissolved materials from water, and in some cases from organic material. Weathering breaks down
rocks into small mineral particles, which collect together as sediment. As time passes, these sediments build up in
layers, eventually forming sedimentary rock.

The sediments are made up of mineral particles of different sizes. The smallest are clays, followed by silts, and then
sands. These particles are very important in the formation of soils. Streams and rivers transport the particles and
deposit them as sediment. With each new deposit, the older layers are pressed down, becoming more compact and
harder, which leads to the formation of sedimentary rock.

Metamorphic rocks form when existing rocks are subjected to extreme heat and pressure. Under these conditions,
the structure of the rock changes. The changes may be chemical, physical, or a combination of both.

Both sedimentary rocks and igneous rocks can be transformed into metamorphic rocks, and even one metamorphic
rock can change into another. Compared to sedimentary rocks, metamorphic rocks are usually harder.

At the beginning, when Earth’s crust first developed, all rocks were igneous. Over time, these rocks were gradually
eroded, producing small particles that created sediment. Layers of this sediment built up to form sedimentary rocks.
The movement of Earth’s crust generates both the heat and the pressure that are necessary for the formation of
metamorphic rock. All rock types continue to be broken down and formed again in a continuous process known as
the rock cycle.

The Rock Cycle (Key Points)

 Rocks are constantly changing through natural processes.

 Weathering breaks down exposed rock at Earth’s surface. This may be:

 Biological (plant growth, animal movement),

 Chemical (reaction with acidic or alkaline water),

 Physical (wind, water, or temperature changes).

When broken rock is moved, the process is erosion; when it is carried elsewhere, it is transportation.

When water slows or wind drops, particles settle. This is called deposition and sedimentation.

Over time, sediments build up in layers. Compaction presses the lower layers, and cementation glues the particles
with minerals dissolved in water, forming sedimentary rock.
When sedimentary or igneous rocks are exposed to heat and pressure underground, they become metamorphic
rocks.

At very high temperatures, rocks melt to form magma.

When magma cools and crystallises, it forms igneous rock.

Igneous rocks can cool rapidly at the surface (small crystals, e.g., basalt) or slowly below the crust (large crystals, e.g.,
granite).

The Rock Cycle (Key Points)

Rocks are constantly changing through natural processes.

Weathering breaks down exposed rock at Earth’s surface. This may be:

Biological (plant growth, animal movement),

Chemical (reaction with acidic or alkaline water),

Physical (wind, water, or temperature changes).

When broken rock is moved, the process is erosion; when it is carried elsewhere, it is transportation.

When water slows or wind drops, particles settle. This is called deposition and sedimentation.

Over time, sediments build up in layers. Compaction presses the lower layers, and cementation glues the particles
with minerals dissolved in water, forming sedimentary rock.

When sedimentary or igneous rocks are exposed to heat and pressure underground, they become metamorphic
rocks.

At very high temperatures, rocks melt to form magma.

When magma cools and crystallises, it forms igneous rock.

Igneous rocks can cool rapidly at the surface (small crystals, e.g., basalt) or slowly below the crust (large crystals, e.g.,
granite).
Permeability: how easily water passes through pore spaces in rocks/soils.

Permeable rocks: have interconnected pores → water and gases pass through easily. Examples: limestone,
sandstone (sedimentary).

Impermeable rocks: few pore spaces → water does not pass through easily. Examples: igneous, metamorphic, shale
(sedimentary).
(Extraction of Rocks, Ores and Minerals)

An ore is a rock that contains valuable minerals and metals. These provide materials for everyday life. Coal and oil
supply energy and chemicals for industry. Metallic ores give metals and alloys for products like computers, mobile
phones, cars, wires, and batteries. Rocks and their products are also widely used in construction.

Methods of Extraction

There are three main ways of extracting rocks, ores, and minerals:

Surface extraction – mining at Earth’s surface.

Sub-surface extraction – removing material from below the surface.

Biological extraction – using organisms such as plants or bacteria.

---
Surface Extraction

Open-pit mining (opencast or open-cut mining): Used when deposits are close to the surface, often under a layer of
waste rock called overburden. The overburden is removed and stored to help restore the land later. The mine is dug
in benches (steps), with sloping walls to reduce rockfalls. Roads are created to remove both minerals and
overburden. Similar methods are used for extracting sand, gravel, and stone for construction.

Strip mining: Used for ores in horizontal layers or seams, such as coal near the surface. The overburden is removed
and machines cut out the ore in strips.
---
Sub-surface Extraction

Used when deposits are too deep for surface mining. Tunnels are dug depending on the geology and the position of
deposits.

Horizontal tunnels are dug directly into a seam (e.g., coal in a hillside).

Sloping tunnels reach deeper deposits. Machinery moves down while minerals and waste are brought up.

Vertical shafts are used for the deepest deposits, with horizontal galleries dug into the minerals. Shaft mining is
expensive and only used for large, valuable deposits.

Compared with open-pit mining, shaft mining is more difficult and dangerous, needing fresh air, water drainage, and
facing risks such as tunnel collapse, poisonous gases, explosions, and fires.
---
Biological Extraction

This uses living organisms and causes less environmental damage, though it yields less material and takes longer. It is
especially useful for low-concentration ores.

Phytomining: Certain plants absorb metals from soil through their roots (bioaccumulation). The plants are harvested,
burned, and the metals extracted from the ash. This is slow but useful for low metal concentrations.

Bioleaching: Certain bacteria break down low-grade ores (e.g., copper) into an acidic solution containing metal ions.
The metal can then be chemically extracted. This process is slow, and the acidic solution can cause environmental
problems if not controlled.
Permeability: how easily water passes through pore spaces in rocks/soils.

Permeable rocks: have interconnected pores → water and gases pass through easily. Examples: limestone,
sandstone (sedimentary).

Impermeable rocks: few pore spaces → water does not pass through easily. Examples: igneous, metamorphic, shale
(sedimentary).

1. Exploration: Mining starts with locating deposits, which is challenging. Success rates are low, around 1 in 100 for
common ores and 1 in 1000 for rare metals like gold. Geologists study rock types, take samples, and test them,
sometimes using aerial surveys to find promising areas.

2. Geology: The type and structure of rocks determine if mining is safe and feasible. Minerals are often concentrated
in layers called seams, and the accessibility of these seams affects extraction methods and costs.
3. Accessibility and Terrain: Even rich deposits may be difficult to mine if the area is remote or lacks suitable roads.
Rough terrain or deep deposits require specialist equipment, increasing costs and technical challenges.

4. Quantity and Quality of Deposit: Mining is expensive, so deposits must be large and high-quality to be profitable.
High-grade ores yield more metal per tonne, while low-grade ores produce less profit due to similar processing costs.
Even rich gold deposits produce large amounts of waste because the percentage of metal is tiny.

5. Climate and Weather: Harsh climates like permafrost or deserts make mining more difficult and costly. Special
equipment and higher wages may be needed, but operations may continue if profits are high enough.

6. Environmental Impact Assessment

Mining damages vegetation, habitats, and can cause pollution. Governments require companies to conduct an
environmental impact assessment (EIA) and show how they will minimize harm. Compliance can be costly,
influencing the decision to mine.

7. Cost, Profit, Supply, and Demand

Extraction depends on costs, profits, and market demand. If production costs exceed selling prices, mining may be
reduced. Minerals are non-renewable, so scarcity can raise prices, making previously unviable deposits profitable.
[5:23 pm, 17/08/2025] BHUVANESHWARI: Environmental Impacts

Mining causes large-scale habitat destruction, reducing biodiversity. It also pollutes air, land, and water, and people
living nearby experience noise and visual pollution.

Ecological Impacts

Vegetation is cleared for extraction, affecting plants and the animals that rely on them. Mine waste can destroy
habitats over time, and deep mining can produce unstable waste heaps.

Noise Pollution

Surface mining is particularly noisy due to explosives and large machines, disturbing wildlife and human health. Deep
mining usually produces less noise.

Water Pollution: Water passing through mine waste can become acidic and toxic, killing aquatic organisms. Toxic
metals can accumulate in animals and increase up the food chain, affecting ecosystems and contaminating drinking
water.

Land Pollution and Waste Management: Mining waste and dust degrade land and soil quality, reduce plant growth,
and can be toxic to humans. Visual pollution is common but can be partially restored after mining. Safe waste
storage is now crucial.

Economic Impacts: Mining provides employment, generates taxes, and can boost local and national economies.
Additional jobs are created if minerals are processed locally. However, some local people may lose land or
livelihoods.

Social Impacts: Mining improves infrastructure, schools, healthcare, and community facilities. But population growth
can create housing shortages, force relocation, and threaten cultural identit

Land Restoration: Land restoration after mining involves reshaping the terrain with mining waste and refilling pits to
match surrounding landscapes. Topsoil is added or imported to support plant growth. Toxic substances are treated
using bioremediation, where organisms break down harmful chemicals. Once the soil is safe, trees are planted to
stabilize the land, prevent erosion, and provide habitats for wildlife, helping re-establish a functional ecosystem
close to its natural state.

Repurposing Land: Damaged mining sites can be repurposed for environmental or practical use. Large pits may be
filled with water to form reservoirs for irrigation or drinking supplies. Restored land can become nature reserves to
increase biodiversity or recreational areas like parks and lakes. Some pits are converted into landfills, covered with
soil, and planted with trees. Repurposing ensures even altered landscapes provide ecological, social, and economic
benefits.
Land Restoration:

Benefits:

Allows natural ecosystems to re-establish.

Stabilizes soil and supports plant and animal life.

Reduces long-term environmental damage.

Limitations:

Time-consuming process.

Requires ongoing monitoring for toxic substances.

Full original habitat may not be completely restored.

Repurposing Land:

Benefits:

Provides faster solutions for damaged sites.

Can create reservoirs, recreational areas, or nature reserves.

Landfills help manage household and industrial waste.

Limitations:

Does not fully restore the original ecosystem.

Landfills can produce methane and risk water pollution.

Some environmental impacts remain despite repurposing.