Weathering, Soil Formation, and Soil Science Fundamentals

Vocabulary flashcards covering key terms related to rocks, minerals, soil formation, soil properties, chemistry, biology, and fertility, designed to aid exam preparation.

Study of rocks, focusing on their composition, structure, and origin.

Petrology

Aggregate of one or more minerals in varying proportions.

Rock

Rock formed by solidification of molten material such as magma or lava.

Igneous Rock

Igneous rock that solidifies below the surface; slow cooling produces coarse texture (e.g., granite).

Intrusive Igneous Rock

Igneous rock that solidifies at the surface; rapid cooling produces fine texture (e.g., basalt).

Extrusive Igneous Rock

Coarse-grained texture characteristic of intrusive igneous rocks.

Phaneritic Texture

Fine-grained texture characteristic of extrusive igneous rocks.

Aphanitic Texture

Igneous texture with large phenocrysts embedded in a finer groundmass.

Porphyritic Texture

Rock formed by compaction and cementation of sediments or organic remains.

Sedimentary Rock

Collective processes of weathering, transport, and deposition of sediments (steps 1–3).

Sedimentation

Compaction and cementation that convert sediments into solid rock (step 4).

Lithification

Rock altered in structure or composition by heat and pressure.

Metamorphic Rock

Continuous transformation of igneous, sedimentary, and metamorphic rocks through geologic time.

Rock Cycle

Mineral crystallized directly from cooling magma; source of sand and silt (e.g., olivine).

Primary Mineral

Mineral formed by weathering of pre-existing minerals; source of clay (e.g., kaolinite).

Secondary Mineral

Sequence describing mineral crystallization order as magma cools.

Bowen’s Reaction Series

Left branch of Bowen’s series with olivine→pyroxene→amphibole→biotite; high Fe & Mg.

Discontinuous Series

Right branch of Bowen’s series where plagioclase changes from Ca-rich to Na-rich.

Continuous Series

Late-stage minerals rich in silica and poor in Fe, Mg, and Ca.

Residual Phase (Bowen)

Breakdown of rocks at Earth’s surface by physical, chemical, and biological processes.

Weathering

Mechanical fragmentation without chemical change (e.g., exfoliation, freeze-thaw).

Physical Weathering

Sheeting or cracking from pressure release during uplift and erosion.

Exfoliation

Expansion of water on freezing widens rock cracks.

Freeze-Thaw

Rock cracking due to repeated heating and cooling.

Thermal Expansion

Surface smoothing from collision of rock particles.

Abrasion

Alteration of mineral chemistry (e.g., oxidation, hydrolysis).

Chemical Weathering

Reaction with oxygen involving electron loss (e.g., magnetite→hematite).

Oxidation (Weathering)

Removal of oxygen with electron gain.

Reduction (Weathering)

Reaction of minerals with water causing decomposition and new clay formation.

Hydrolysis

Incorporation of water molecules into mineral structure without destroying it.

Hydration

Reaction of carbonic acid with minerals, common in limestone.

Carbonation

Rock breakdown by living organisms (e.g., root wedging, animal burrowing).

Biological Weathering

Growth of roots in cracks, widening them as roots enlarge.

Root Wedging

Natural body of minerals, organic matter, water, and gas capable of supporting plants and exhibiting horizons.

Soil (Soil Survey Staff, 1999)

Russian scientist regarded as the Father of Soil Science.

Vasily Dokuchaev

Developed the five soil-forming factors model (CLORPT).

Hans Jenny

Acronym for Climate, Organisms, Relief, Parent material, Time—five factors of soil formation.

CLORPT

Downward translocation of soluble substances by water.

Leaching

Mixing of soil by living organisms such as earthworms or termites.

Bioturbation

Layer of soil parallel to the surface with distinct physical, chemical, and biological properties.

Soil Horizon

Surface layer of organic material at various decomposition stages.

O Horizon

Mineral topsoil enriched with dark organic coatings.

A Horizon

Eluviation zone where clay, organic matter, and Fe/Al oxides are leached; light colored.

E Horizon

Subsoil zone of illuviation where leached materials accumulate.

B Horizon

Partially weathered parent material outside active soil-forming zone.

C Horizon

Unweathered, consolidated bedrock.

R Horizon

True soil comprising O, A, E, and B horizons—zone of pedogenic activity.

Solum

Movement of material OUT of a soil horizon.

Eluviation

Movement of material INTO a soil horizon.

Illuviation

Processes that differentiate initial material into distinct soil horizons.

Horizonation

Processes that mix or disturb horizons, slowing horizon differentiation.

Haploidization

Input of materials to soil (e.g., littering, melanization).

Addition (Soil Process)

Losses from soil such as erosion or leaching.

Removal (Soil Process)

Chemical or biological changes within soil (e.g., humification).

Transformation (Soil Process)

Movement of soil constituents within the profile (e.g., salinization, lessivage).

Translocation

Accumulation of soluble salts in soil horizons.

Salinization

Build-up of exchangeable sodium on soil colloids.

Alkalization (Solonization)

Leaching of sodium ions and salts from a soil horizon.

Dealkalization (Solodization)

Migration of Fe, Al, and organic matter leaving silica-rich E horizon.

Podzolization

Leaching of silica resulting in Fe/Al oxide enrichment in tropical soils.

Laterization

Release and oxidation of iron giving soils brown color.

Braunification

Advanced iron oxidation imparting reddish-brown hues.

Rubification

Intense iron accumulation giving red soil colors.

Ferrugination

Reduction of iron under waterlogged conditions producing gray-blue colors.

Gleization

Washing of fine clay down cracks and voids.

Lessivage

Accumulation of calcium carbonate in soil horizons.

Calcification

Mixing of soil by physical or biological agents.

Pedoturbation

Soil mixing by animals.

Faunalturbation

Soil mixing by plant roots.

Floralturbation

Soil churning from clay shrink-swell cycles.

Argilliturbation

Soil mixing by freeze-thaw action.

Cryoturbation

Compact, often spherical mass of cemented mineral matter in soils or sediments.

Concretion

In-situ chemically weathered rock retaining original structure.

Saprolite

Relative proportion of sand, silt, and clay particles.

Soil Texture

Largest soil separate, 0.05–2 mm, gritty, non-plastic.

Sand

Intermediate soil separate, 0.002–0.05 mm, smooth, slightly plastic.

Silt

Smallest soil separate, <0.002 mm, sticky and plastic when moist.

Clay

Quantitative technique for determining soil texture using Stoke’s Law sedimentation.

Hydrometer Method

Principle that larger particles settle faster than smaller ones in a fluid.

Stoke’s Law

Chemical (e.g., sodium hexametaphosphate/Calgon) used to separate soil particles for analysis.

Dispersing Agent

Substances like clay, organic matter, or Fe/Al oxides that bind particles into aggregates.

Flocculating Agent

Arrangement of soil particles into aggregates.

Soil Structure

Resistance of soil aggregates to disruptive forces such as water erosion.

Aggregate Stability

Small, crumb-like aggregates common in A horizons; high permeability.

Granular Structure

Angular or subangular aggregates typical of B horizons.

Blocky Structure

Vertical column-like aggregates in B horizons with moderate permeability.

Prismatic Structure

Prisms capped with rounded tops, common in arid soils with salt accumulation.

Columnar Structure

Thin, flat plates formed by compaction; slow permeability.

Platy Structure

Loose particles lacking aggregation, as in sands.

Single Grained

Homogeneous soil mass with no visible structure.

Massive Structure

Intentional destruction of soil structure by tillage in flooded conditions to create an impervious layer.

Puddling

Mass of dry soil per unit total volume; indicator of compaction and porosity.

Bulk Density

Mass of soil solids per unit solid volume; ~2.65 g cm⁻³ for mineral soils.

Particle Density

Percentage of total soil volume that is pore space.

Porosity

Downward entry of water at the soil surface.

Infiltration

Downward movement of water through soil layers due to gravity.

Percolation

Ability of soil to transmit water or fluids through pores.

Permeability

Force with which water is held in soil; inverse of water availability.

Soil Moisture Tension

Soil moisture content after gravitational water drains (~1/3 bar).

Field Capacity

Soil moisture level at which plants cannot extract water (~15 bar).

Permanent Wilting Point