On the afternoon of October 15th 1987, ten bluestones were sampled by Dr. Richard Thorpe by drilling cores 1" diameter by about 2" deep using a diamond drill bit. A further five bluestones had sample flakes removed from them.
For full details see "Geochemistry, Sources and Transport of the Stonehenge Bluestones", O. Williams-Thorpe & R. S. Thorpe (Proceedings of the British Academy, 77, pp 133-161, 1991)
Stone 65 shows evidence of where a core extraction was attempted.
The ring where the core drill was used is clearly visible in the next photo: