How do I identify a sedimentary rock?

Decide whether visible detrital clasts dominate or whether the rock is chemical, biochemical, or organic. For clastic rocks, use grain size first, then rounding, sorting, fissility, and composition.

What grain sizes define common clastic sedimentary rocks?

Gravel is at least 2 mm, sand is about 0.0625 to 2 mm, silt is about 0.004 to 0.0625 mm, and clay is finer than 0.004 mm.

What is the difference between conglomerate and breccia?

Both contain gravel-sized clasts. Conglomerate has predominantly rounded clasts, whereas breccia has predominantly angular clasts.

What is the difference between shale and slate?

Shale is sedimentary and commonly splits along bedding. Slate is metamorphic and splits along slaty cleavage, which can cut across original bedding.

Can I identify limestone with acid?

Calcite-rich limestone commonly effervesces in cool dilute acid, but test conditions and mixed composition matter. Use only an authorized procedure with eye protection.

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Sedimentary Rock Identification Chart

Sedimentary rocks form from deposited material that is compacted, cemented, precipitated, or accumulated through biologic and organic processes. A defensible hand-sample classification starts by separating clastic material from chemical, biochemical, and organic material. Clastic names begin with grain size: gravel-sized clasts at least 2 millimetres across form conglomerate when predominantly rounded and breccia when predominantly angular; sand-sized grains about 0.0625 to 2 millimetres form sandstone; silt-sized grains about 0.004 to 0.0625 millimetres form siltstone; and finer mud-sized rocks include shale, mudstone, and claystone. Fissility helps separate shale from more blocky mudrock, but metamorphic slaty cleavage is an important look-alike. Carbonate rocks include limestone and dolostone and may preserve fossils, ooids, crystalline texture, or dense micrite. Chert is a hard microcrystalline silica rock with conchoidal fracture. Rock gypsum and rock salt are evaporite candidates; coal-family rocks concentrate organic material. Bedding alone does not establish a sedimentary origin, and a rock name does not prove a depositional environment. GeoMiner's private selector accepts only bounded visible-clue and supporting-observation groups and sends no specimen name, free text, photo, location, exact colour, fossil identity, measurements, or detailed test results. Do not taste, lick, grind, inhale dust, heat, or casually acid-test an unknown. Formal petrography, grain-size analysis, stratigraphic work, or chemistry may be required.

Quick ID for clastic rocks — Carry a broad detrital texture into the account-free property key.
Conglomerate vs breccia — Use representative rounded versus angular gravel-sized clasts without assuming origin.
Sandstone vs siltstone — Compare dominant grain size, hand-lens visibility, and mixed fine-clastic boundaries.
Siltstone vs shale — Combine silt-sized texture with repeated bedding-parallel fissility and naming limits.
Shale vs mudstone — Separate fissile from blocky mudrock while stating the terminology convention.
Shale vs slate — Separate sedimentary fissility and bedding from metamorphic slaty cleavage.
Marble vs limestone — Compare recrystallized metamorphic texture with fossils, pores, grains, and bedding.
Rock reference library — Verify candidates against the source-backed rock catalogue.
Complete rock and mineral chart — Test whether a sedimentary family is plausible before choosing a name.

Verification resources

Cross-check terminology, classification, methods, and safety with these authoritative external resources.

undefined. Sedimentary origins, bedding, clastic grain-size names, and biologic or chemical examples.
undefined. Standard Wentworth boundaries for gravel, sand, silt, and clay size fractions.
undefined. Observable texture, composition, and origin as foundations for classifying sedimentary rocks.
undefined. Clastic, biologic, and chemical sedimentary groups and the role of deposition and lithification.
undefined. Definitions for claystone, siltstone, sandstone, conglomerate, shale, mudstone, and limestone.
undefined. A teaching classification combining clastic grain size with chemical, biochemical, and organic composition.
undefined. A classroom sedimentary identification chart organized by grain size and composition.

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Common questions

How do I identify a sedimentary rock?: Decide whether visible detrital clasts dominate or whether the rock is chemical, biochemical, or organic. For clastic rocks, use grain size first, then rounding, sorting, fissility, and composition.
What grain sizes define common clastic sedimentary rocks?: Gravel is at least 2 mm, sand is about 0.0625 to 2 mm, silt is about 0.004 to 0.0625 mm, and clay is finer than 0.004 mm.
What is the difference between conglomerate and breccia?: Both contain gravel-sized clasts. Conglomerate has predominantly rounded clasts, whereas breccia has predominantly angular clasts.
What is the difference between shale and slate?: Shale is sedimentary and commonly splits along bedding. Slate is metamorphic and splits along slaty cleavage, which can cut across original bedding.
Can I identify limestone with acid?: Calcite-rich limestone commonly effervesces in cool dilute acid, but test conditions and mixed composition matter. Use only an authorized procedure with eye protection.

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Sedimentary Rock Identification Chart

Test a sedimentary shortlist against alternatives

Verification resources

Common questions