What is the difference between sedimentary and metamorphic rocks?

Answer 1

Geologists categorize rocks into three basic groups, of which sedimentary and metamorphic are two. Igneous is the third. Sedimentary rocks are laid down in layers of sediments such as mud, silt and sand that accumulate and harden over time. Igneous rocks are formed from the solidification of lava or magma. Metamorphic rocks are a bit of a combination. They are sedimentary rocks or igneous rocks that have been deformed and changed by high pressure and temperature deep in Earth, or by contact with, or close proximity to a magmatic intrusion.

A simple diagram showing the rock cycle with the processes that link sedimentary and metamorphic rocks as well as a simple diagram showing how metamorphic rocks are named and the rock types from which they are formed as well as A glossary of geological terms is also available. Please see the related links section.

Answer 2

Sedimentary rock is formed from various sizes of rock or rock particles that have been deposited by wind or water over time. The weight and pressure of subsequent deposits results in the squeezing out of water from the lowest depositional layers, and these layers may become cemented together by a number of minerals that have been in the solution and have then crystallized.

Metamorphic rock is formed from a change in an existing parent rock, or protolithic rock. The changes are usually in the arrangement or composition of the minerals that make up the parent rock into new arrangements or minerals. The change occurs as a result of contact with molten material over small or wide geographic scales, or from pressure and/or heat derived from depth of burial or mountain building processes.

Answer 3

There is only one similarity: regional metamorphism and the formation of sedimentary rock both require high pressure.

The differences are:

• All metamorphism requires heat, whereas if heat is too excessive, a sedimentary rock is not formed, but an igneous or metamorphic one.
• Sedimentary rocks are made of fragments, whereas metamorphic rocks are from existing rocks
• Metamorphism requires the partial recrystallisation of the old rock, but in a sedimentary rock there are no crystals, so no recrystallisation takes place
• Thermal metamorphism requires no pressure, only heat, whereas all sedimentary rocks are formed at depth

In summary, sedimentary rocks don't require heat, metamorphic ones do, sedimentary rocks are made of fragments of other rocks or minerals, metamorphic rocks are old rocks which have been partially recrystallised, metamorphism can take place on the surface, but sedimentary rocks can't be.