Thank you for the question Mr. Naqvi and answer Mr. Clark, I was also searching the answer for the same. I was also willing to know the quick and in situ way to, distinguish sand, silt and clay in the field. Are they any of the ways how we can separate it easily like from visual investigation (yes of course this needs a lengthy experience)?. For example, I have a site and have to investigate by visual or other simple ways. After knowing whether it's cohesive or non-cohesive, we can follow the Handbook of Geotechnical Investigation and Design Tables by Burt Look for simple insitu tests like thumb penetration, walk over, peg or rod penetration. I shall be thankful for your reply.