Clastic sedimentary rocks are made up of pieces (clasts) of pre-existing rocks. Pieces of rock are loosened by weathering, then transported to some basin or depression where sediment is trapped. If the sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock.
Magma forms from the partial melting of mantle rocks. These little blobs of melt migrate upward and coalesce into larger volumes that continue to move upward. As they rise, gas molecules in the magma come out of solution and form bubbles and as the bubbles rise they expand (as outside pressure gets lower).
I hope this helps When the molten rock cools it forms an igneous rock. Metamorphic rocks can form from either sedimentary or igneous rocks. The sedimentary particles from which a sedimentary rock is formed can be derived from a metamorphic, an igneous, or another sedimentary rock. All three rock types can be melted to form a magma.
