Primary Aggregates are materials extracted directly from the ground in quarries or pits. They can be either sand and gravel, or hard rock.
Hard rock deposits are quarried from a fresh face and broken by mechanical means into aggregate. As aggregates, they are often referred to as crushed rock or by their individual geological names. The rock will pass through several stages of crushing and screening to create the final product.
Sand and gravel has already been broken into pieces by the natural processes of weathering, transported by water or ice, and then deposited in a loose form. Gravel can still be in large pieces, which will need crushing, and usually all the material will need to be washed to remove fine clay particles.