Sandstone!
To a typical field geologist, sandstone is pretty recognizable in hand sample. However, to a mudlogger, sand can mask itself in many different ways. This photo is taken under a microscope at 10x power. This is literally the MUD that a MUDlogger looks at. After washing away all the excess water, additives and fine particles we are left with this beautiful picture. There are 2 distinct colors in this photo: white and brown. There is only one major rock type here: sandstone. The difference between hand sample and mud sample is huge. In a hand sample we often are limited by our hand lenses. They allow us to see grain size and shape but don’t allow us access to the subtleties of the rock. This sample shows an argillaceous sand, or, a very clay-rich sand. It is basically on the line of being called a ‘sandy-shale’ or a ‘shaley-sand.’ The overwhelming amount of visible grains leads me to call this a sandstone, but the amount of brown, caked on mud tells me that a shale bed is neighboring this sand bed. Both above and below this sand, sat shale beds that contaminated the purity of the sand.