Soil Formation and Classification

Vocabulary flashcards covering soil formation factors, rock classification, physical and chemical weathering, soil horizons, and distinct soil types including brown earths, podzols, gleys, and peats.

Parent Material

The geological rock material from which soil develops, determining fundamental characteristics including soil pH, texture, and fertility.

Igneous Rocks

Rocks formed when molten magma cools and solidifies, developing large crystals if cooled slowly or small crystals if cooled quickly.

Sedimentary Rocks

Rocks formed when layers of sediment accumulate on sea or lake beds and are compressed together under pressure over time.

Metamorphic Rocks

Rocks formed when preexisting igneous or sedimentary rocks are subjected to extreme heat and/or pressure, altering them into a new type of rock.

Granite

An igneous rock containing minerals such as quartz, mica, and feldspar; commonly found in Donegal, Galway, and Wicklow.

Basalt

A dark, fine-grained igneous rock found at the Giant’s Causeway in Antrim.

Limestone

A sedimentary rock formed from compressed fossils and shells that leads to alkaline soils; located in the Burren in Co. Clare.

Sandstone

A sedimentary rock formed from accumulated layers of sand that leads to the development of acidic soils.

Marble

A metamorphic rock formed by the transformation of limestone under heat and/or pressure.

Quartzite

A metamorphic rock formed by the transformation of sandstone under heat and/or pressure.

Gneiss

A metamorphic rock formed by the transformation of granite under heat and/or pressure.

Mechanical Weathering

The physical breakdown of parent material and large rock particles into smaller particles without changing their chemical structure.

Chemical Weathering

The breakdown of parent material and large rock particles into smaller particles through chemical reactions.

Freeze-thaw Action

A mechanical weathering process where water enters cracks in rocks, expands upon freezing, and thaws repeatedly, creating pressure changes that cause the rock to shatter.

Abrasion

A mechanical weathering process where rocks collide with one another while being transported by gravity, wind, or water, wearing them down.

Oxidation

A form of chemical weathering where rock minerals react with oxygen and water, such as the oxidation of iron giving rocks a rust color.

Carbonation / Solution

A chemical weathering process where dissolved carbon dioxide in rainwater forms weak carbonic acid that reacts with and dissolves rock.

Hydrolysis

A chemical weathering process in which minerals within rocks break down upon reacting with water.

Soil Profile

A vertical section of soil revealing its five distinct layers or horizons: O, A, B, C, and R.

O Horizon

The uppermost layer of a soil profile, composed entirely of organic matter.

A Horizon (Topsoil)

The upper mineral layer of soil that contains both organic matter and minerals derived from parent material.

B Horizon (Subsoil)

The soil layer situated below the topsoil, rich in minerals that have leached downwards through the O and A horizons.

C Horizon

The soil horizon mostly consisting of weathered parent material from which the upper soil has developed.

R Horizon (Bedrock)

The solid, unweathered mass of parent material beneath the soil profile that is not considered soil.

Brown Earths

Fertile, free-draining soils formed over limestone parent material; characterized by indistinct, blended horizons that are uniform in color throughout.

Podzol Soils

Acidic soils formed over acidic parent material, characterized by a bleached A horizon, an accumulation of minerals in the B horizon, and an impermeable iron pan.

Podzolisation

The soil-forming process in acidic conditions where acidic leaching leaves a bleached A horizon and causes minerals to form an impermeable iron pan in the B horizon.

Iron Pan

An impermeable layer of cemented minerals located in the B horizon of podzols that prevents water drainage and causes waterlogging unless shattered with a subsoiler.

Gley Soils

Waterlogged soils found in valleys or areas with high water tables, characterized by poor natural drainage and a mottled appearance in the B horizon.

Gleisation

The soil-forming process occurring under waterlogged conditions where mineral oxidation and reduction give the B horizon a distinct mottled appearance.

Basin Bog

A peatland formed when partially decomposed organic material accumulates under anaerobic conditions within a lake.

Raised Bog

A peatland formed when organic matter deposition in a basin bog continues to accumulate above the water level of the original lake.

Blanket Bog

A peatland that develops across flat or sloping landscapes under conditions of high rainfall and low evaporation.

Agricultural Regions in Ireland

A spatial distribution classifying Irish farming land uses—such as dairying, arable, mixed livestock, grazing, and fringe—based on underlying soil properties.