Quartz crystals are thought to have been drilled out of an historic dolmen in Jersey. The damage to the 6,000-year-old neolithic passage, La Pouquelaye de Faldouet in St Martin, is several inches across and deep.
Residents nearby reported hearing noises on the night of 24 October.
On 31 October, members of Société Jersiaise also found newly drawn graffiti on the stones at Mont Grantez. Anyone who witnessed any suspicious activity is asked to report it to the police.