False-colour scanning electron micrograph of standard filter paper clogged with silt particles after soil-contaminated water was passed through it. Filter paper is used to separate the liquid from the solid parts of a suspension. It is made from wood pulp (in particular that obtained from spruce, poplar, pine and fir trees), hence the presence of the cellulose fibres seen here under the silt. Soil contains gravel, sand, silt & clay. Most of the particles here are silt, with a size range of 2 to 50 micrometres. Gravel & sand would be unlikely to stay suspended in water anyway, while, at this magnification, the clay is probably invisible. Magnification: x60 at 6x4.5cm size.