Soil 1 – Rock Types

There are about 6.8 million hectares in Ireland.

25% of this area is covered with cities, roads and buildings etc. so the remaining 5 million hectares is covered in soil.

This soil varies greatly in depth, composition, fertility, appearance etc.

Soils can be classified as “rich” fertile soils or poor “hungry”

Soils are the medium for the growth of land plants.

All soils come from parent materials. Therefore the type of soil in an area depends on the parent rock.

The condition of the soil is highly dependent on the type of bedrock.

Example: • Soils formed from granite would be acidic (pH

< 7)• Soils from Limestone would be basic.

Drainage depends on the underlying rock.

In Ireland there is a vast range of soil types. They are classified accordingly:

• Residual: materials are rock deposits which weather in situ long enough for soils to develop from them.

• Transported: materials are broken down rock which have been transported some distance by natural forces e.g. wind and water. Soils then develop from transported materials in their new locations. In Ireland ice was the main transporting agent.

• Cumulose: materials are organic materials derived from preserved plant remains. This gives rise to peat soils.

All these parent rocks can be divided into 3 main groups.

IgneousSedimentaryMetamorphic

Igneous Sedimentary MetamorphicGranite Sandstone Marble

Basalt Limestone Slate

First ever rocks formed on the earth (4.5 billion years ago).

Formed when molten lava began to cool, solidify and form rocks.

Igneous rocks are made of the following elements: Oxygen, Silicon, Aluminium, Iron, Calcium, Sodium, Other metals and non-metals.

Characteristics of igneous rocks: acidic soils and fine grained soils.

Examples of Igneous rocks include Granite and Basalt.

Granite is made up of three main components: Feldspar, Mica, and Quartz.

Mica is black and contains the same as Feldspar as well as Fe and Mg. Quartz contains both Feldspar and Mica.

Tends to form an acid solution. Is crystalline in structure and looks like glass. Feldspar is pink in colour and has K, Al Si. Basalt and Granite are formed from the same

material and differ only due to how they cooled down. Granite cooled very slowly gave very large and has large crystals. Whereas Basalt cooled faster and lots of small crystals.

Formed when, sediments of different rocks, shells and bones of animals joined together.

Examples of sedimentary rocks are Sandstone, Limestone and Shale.

Sandstone is formed by sediments of quartz, (broken up by water, heat and frost as well as Glacial forces).

Characteristics of Limestone rock: alkaline soils and texture in between sandy (sandstone) and clayey (shale).

Limestone (CaCO3 – Calcium Carbonate) This is a highly desirable rock type. Limestone is formed by the fusing of

pieces of sea shells and other materials containing Calcium carbonate (CaCO3),

It forms an alkali solution in water. Its pH provides the optimum range for

plant growth – 7.5. It is also a permeable rock.

These rocks arise from sedimentary rocks when they are exposed to pressure and heat.

Examples are Slate (changed from shale) and marble (from Limestone)