Why rock gold mining stones need fully crushed and grinding before into Knelson series centrifuge

It's very common to see rock gold mine in natural mine, before it's getting separated by knelson series centrifuge need fully crushed and grinded by mining machinery.And what's the direct reason of doing this?

The get the particle fully crushed and free monomor is a must,then into classifying system to get the useful material finally to get the material into concentrator machine for gold concentrate.The gravity separating need a fully separated particle the smaller in size,the better in separating. It can also make the whole plant in more efficient and reduce the clay during the separating process.