There are three basic types of rock:

IGNEOUS rocks are formed when molten rock cools, it is found in two major forms. Basalt is lava from a volcano that has been spewed out and cooled on the surface. Granite is formed when magma, found in the earth's mantle, rises closer to the surface then cools slowly inside the earth's crust.

SEDIMENTARY rocks are formed when weathered or eroded material is deposited on the bottom of rivers, lakes, seas and oceans. Over long periods of time this sediment is buried and compressed. Often plant and animal material is buried along with it and is found as fossils. Coal, limestone and sandstone are sedimentary rocks.

METAMORPHIC rocks are formed when rock is structurally altered through intense heat and pressure. Marble is produced when limestone is subjected to these stresses.

Weathering

Trapped in each type of rock are different minerals vital for survival. All rocks undergo weathering that continuously breaks them down into smaller particles. Natural weathering happens in three different ways:

Physical weathering causes rocks to break up through the action of winds and rain. In addition water in cracks expands when freezing breaking rocks apart and thawing carries particles away.

Chemical weathering slowly decomposes rocks by chemical reactions altering the minerals reducing the way they are bonded together. Oxygen weakens rocks by reacting with the minerals to form oxides.

Biological weathering is the action of plants and animals upon rock. For example roots force rocks apart as they grow, animals scrape and dig whilst looking for food.

Soil is made up of rock particles, plant and animal material, nutrients, air and water. Dissolved in the water are the minerals from rocks essential for plant growth. The mineral elements needed by plants are absorbed and a cycle takes place - weathering from rock - uptake (absorption) by plants into the plant's structure -death and decomposition of the plant releases the minerals back into the soil for reuse by other plants. Potassium and phosphorous are examples of minerals that follow these cycles.

Some soil is naturally washed into rivers and lakes and eventually to seas where it remains on the ocean beds to become the sedimentary rocks of the very distant future so continuing the cycle with new rock formation.

Human Activities

Human activities such as intensive farming, deforestation and agrochemicals cause soil to become unstable and more easily washed away and deposited at river estuaries and eventually swept out to sea. It is estimated that the earth is losing 30,000 million tonnes of soil per year in this way, which is not recoverable. Soils are being washed away faster than new rocks form. Once the soil structure is weakened desertification occurs as soils are rapidly removed through the actions of wind and rain.

In addition, mining removes rocks from the natural cycle and dramatically alters ecosystems. Coal is mined for fuel, limestone for road chippings and cement, sandstone and marble for buildings are a few examples. Minerals and elements are also mined and extracted from rock structures.