Clive, natural? Go get a lump of mica. In its natural state, it resembles the form or look of t-grains in a photomicrograph. So nature creates what man makes in a lab.
As for lying flat, yes they do. They come out of the hopper flat, they are coated flat and compress down into a flat layer. In fact, they are so flat that on small rollers in some cameras, the grains can crack going around the bend unless the right "lubricants" are used in the emulsion.
They develop to give silver images that are similar to K grains, but they stop more light and thus give higher speed with lower grain.