How do metamorphic rocks differ from igneous and sedimentary rocks?
The correct answer and explanation is :
Metamorphic rocks differ from igneous and sedimentary rocks in terms of their formation processes, mineral composition, and texture. Here’s a breakdown of each:
Formation:
- Metamorphic rocks form when existing rocks—either igneous, sedimentary, or other metamorphic rocks—undergo high heat, pressure, or chemical processes that cause them to change. This process, called metamorphism, occurs deep within the Earth’s crust or at tectonic plate boundaries. The original rock, called the protolith, is altered by temperature and pressure conditions over millions of years. The metamorphic process does not involve melting but rather a solid-state transformation.
- Igneous rocks, on the other hand, form from the cooling and solidification of molten rock (magma or lava). They are classified into two types: intrusive (formed inside Earth, like granite) and extrusive (formed on Earth’s surface, like basalt). The cooling process determines the mineral composition and texture of the rock.
- Sedimentary rocks form from the compaction and cementation of sediments—tiny particles of rock, mineral fragments, and organic material—that accumulate over time. This happens mostly on the Earth’s surface, in environments like rivers, oceans, and deserts. Common examples include sandstone, limestone, and shale.
Mineral Composition and Texture:
- Metamorphic rocks often have a foliated texture (layered or banded structure), where minerals are aligned in parallel layers due to directional pressure, or a non-foliated texture, where the minerals are randomly arranged (e.g., marble, which forms from limestone).
- Igneous rocks have a crystalline texture, where minerals crystallize from the molten material, either forming large crystals (in intrusive rocks) or small crystals (in extrusive rocks).
- Sedimentary rocks typically have a clastic texture, consisting of visible fragments of other rocks or organic material, cemented together over time.
In summary, metamorphic rocks differ from igneous and sedimentary rocks in how they are formed, the processes involved, and their final structure and mineral composition.