Cornflour is made from finely ground corn; thats what it looks like to me.. It's used in cooking as a thickening agent, and also in HP Sauce.

What I used to do with it though is to make a saturated solution of it with cold water. This has the interesting properties of flowing like a liquid, but fracturing like a solid when pushed around too fast and is an example of an iostropic liquid (in contrast to a thixotropic liquid like tomato ketchup.