Soil Formation and Types of Soil Flashcards

Vocabulary flashcards covering rock categories, rock descriptions, soil origins, transported soils, and USCS soil classification types.

Igneous Rocks

Rocks formed by the solidification of molten magma ejected from deep within earth’s mantle.

Sedimentary Rocks

Rocks formed by the accumulation or deposition of mineral or organic particles at the surface of the Earth, followed cementation.

Metamorphic Rocks

Rocks formed when existing rock is transformed physically or chemically at elevated temperature.

Quartz – Syenite

A pinkish-grey, reddish-tan, or buff grey rock with a medium-to-coarse-grained texture.

Basalt

A dark grey to black rock that weathers to reddish-brown or dark green, featuring a fine-grained texture.

Granodiorite

A coarse-grained rock with a salt and pepper appearance, being medium to light grey with dark specks.

Pyroxenite

A dark olive green, dark brown, or black rock with a coarse-grained texture.

Pumice

A light grey, off-white, cream, or pale tan rock with a sponge-like structure.

Phyllite

A silvery-grey, greenish-grey, or iridescent pearl grey rock with phyllitic foliation, characteristically featuring wrinkled or wavy surfaces with a pronounced silky, satiny sheen.

Gneiss

A coarse-grained foliated rock with alternating light grey/pink and dark charcoal/black stripes.

Eclogite

A medium-to-coarse-grained rock with a striking Christmas rock contrast, composed of a bright green matrix studded with reddish-pink crystals.

Glaucophane Schist

A well-foliated, fine-to-medium-grained rock with a distinctive lavender-blue, dark blue-grey, or indigo color.

Chalk

A bright pure white or off-white, extremely fine-grained, soft, porous rock that leaves white powder when rubbed.

Breccia

A clastic, coarse-grained rock with sharp, angular, jagged rock fragments set in a fine matrix.

Conglomerate

A clastic, coarse-grained, clast-supported rock featuring rounded to well-rounded pebbles and multi-colored gravel clasts set in a tan, grey, or reddish sand matrix.

Arenite

A pure white, cream, or light grey clastic, grain-supported sandstone with minimal mud matrix.

Residual Soils

Soils that remain at their place of origin directly above the parent rock.

Transported Soils

Soils that have been eroded and moved from their original location by agents like water, wind, ice, or gravity.

GW: Well-Graded Gravel

Very coarse, clean, interlocking, angular to sub-rounded rock fragments with a wide, continuous distribution of sizes (fine to coarse gravel); non-plastic with high interparticle friction.

GP: Poorly Graded Gravel

Uniform coarse texture dominated by a single particle size (or gap-graded missing intermediate sizes); clean feel with large, open void spaces between fragments; non-plastic.

GM: Gravel with Silty Fines

Coarse gravel matrix coated or infiltrated with fine, flour-like silt; dry hand samples feel dusty/gritty, and moist samples show minimal stickiness with low to no plasticity.

GC: Gravel with Clayey Fines

Hard, coarse gravel fragments firmly bound in a sticky, cohesive clay matrix; plastic when wet, forming hard, cemented lumps when dry.

SP: Poorly Graded Sand

Uniform, gritty feel with a narrow spread of particle sizes (such as dune or beach sand); clean, loose, free-draining grains with zero cohesion or plasticity.

SM: Sand with Silt

Gritty yet noticeably floury or powdery feel when dry; exhibits weak cohesion when damp but breaks apart easily; non-plastic to low-plasticity fines.

SC: Sand with Clay

Gritty sand grains embedded in a highly plastic, sticky clay binder; pliable and moldable when moist, curing into firm, rigid clods when dry.

CH: Fat Clay

Extremely slick, greasy, highly plastic, and intensely sticky when wet; very high dry strength forming rock-hard clods; prone to severe shrinking and cracking upon drying.

Pt: Peat

Highly fibrous, spongy, lightweight, and intensely compressible; composed of mat-like, partially decomposed plant fibers and roots with extremely high moisture retention.

Sandy Loam

Soil that is moderately gritty and contains sufficient silt and clay to form a pliable cast when wet, capable of forming a weak ribbon up to $2.5\,\text{cm}$ long before breaking.

Clay Loam

Soil that is smooth and plastic with a mild underlying grittiness; forms a firm ribbon ($2.5\,\text{cm}$ to $5\,\text{cm}$) that bends moderately before cracking.

Silty Clay

Soil that is extremely smooth, slick, plastic, and sticky when wet; forms long, strong, shiny ribbons ($> 5\,\text{cm}$) with zero gritty feeling.