* Sedimentary Rocks: These rocks are formed from the accumulation and cementation of sediments (like sand, clay, or shells). The grains you see are individual pieces of these sediments.
* Metamorphic Rocks: These rocks are formed when existing rocks (igneous, sedimentary, or other metamorphic rocks) are transformed by heat, pressure, or chemically active fluids. This transformation changes the mineral composition and texture of the original rock.
Instead of "grains," metamorphic rocks often have:
* Foliation: This is a layered or banded appearance caused by the alignment of mineral crystals under pressure. Examples: slate, schist, gneiss.
* Non-foliated: These rocks lack the layered appearance of foliated rocks. The minerals within are more randomly arranged. Examples: marble, quartzite.
So, the "grain" in metamorphic rocks is more about the arrangement of minerals and the texture of the rock, rather than individual sediment particles.
