The final and most mind boggling point of interest at Dyffryn stone circle is a fallen stone which has broken in three pieces, at least from my casual observation. Pictured below you can see the base part of the stone lying across the front of the shot, the middle section is hidden behind it, and the top section can be seen lying on the ground immediately back from the base.
Most curious about this broken stone is its cross sectional shape. From the present view you can make out grooves running across the picture from side to side on the base section of the stone in the front foreground. The next picture shows these far more clearly.