Short answer
Sedimentary rock forms as deposited material accumulates and becomes rock, or as minerals precipitate. Metamorphic rock forms when an older rock changes under heat, pressure or fluids without complete melting. A sedimentary rock can later become metamorphic, so the categories describe stages in a rock’s history. 1 2
Sedimentary rock forms from deposited material; metamorphic rock forms by transformation of existing solid rock.
On this page
At a glance
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| Question | Sedimentary rock | Metamorphic rock |
|---|---|---|
| Main process | Deposition and lithification or precipitation | Solid-state transformation |
| Common clue | Bedding or sediment grains | Recrystallization or foliation |
| Example | Sandstone | Slate or marble |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Sedimentary rock. Rock formed from accumulated sediment or other deposits that become consolidated or chemically precipitated. 1
Metamorphic rock. Preexisting rock substantially changed by heat, pressure, or fluids while remaining largely solid. 2
Key differences
USGS describes sedimentary rocks as products of deposits near Earth’s surface. Metamorphism changes mineral assemblage or texture at elevated conditions, often deeper in Earth. The difference lies in how the present rock formed, not merely the minerals it contains. 1 2
How to tell them apart
Look for bedding, fossils or clastic grains as sedimentary clues; foliation or recrystallized texture may suggest metamorphism. None is universal. Field setting and mineral analysis can resolve ambiguous samples. 1 2
Where they overlap
Both can come from older rocks and both can show layers. A shale can metamorphose into slate, preserving traces of its sedimentary origin while becoming a metamorphic rock. 1 2
Edge cases
Some sedimentary rocks form by chemical or biological processes rather than compacted sand. Low-grade metamorphism can preserve original bedding; high-grade changes can erase it. Multiple histories may require a more specific name. 1 2
Why the distinction exists
Rock classification records formation and transformation, helping reconstruct depositional environments and later tectonic or thermal events. 1 2
Common misconceptions
Visible stripes do not guarantee a rock is sedimentary; metamorphic foliation can also produce bands. 1 2
Examples
Sand layers compacted and cemented into sandstone make sedimentary rock. Heat and pressure changing shale to slate make metamorphic rock. 1 2
Sources
Sources checked October 3, 2026.
- USGS — What Are Sedimentary Rocks?. Formation of sedimentary rocks.
- USGS — What Are Metamorphic Rocks?. Process of metamorphism.