The Thurgartstone or Ogrestone is a prominent glacial erratic stone near Dunlop in East Ayrshire, Scotland. The Thurgartstone stands in a field at Brandleside Farm and is thought to have been a rocking stone at one time, but it no longer moves due to a build up of soil beneath.

Rocking stones are large stones that are so finely balanced that the application of just a small force causes them to rock. Typically, rocking stones are residual corestones formed initially by spheroidal weathering and have later been exposed by erosion or glacial erratics left by retreating glaciers. Natural rocking stones are found throughout the world. A few rocking stones might be man-made megaliths.