A historic rock called Hertfordshire Puddingstone has been stolen from the Museum of St Albans.

Hertfordshire Puddingstone is a naturally occurring conglomerate consisting of rounded flint pebbles bound in silica cement, found mostly within the county.

It is thought to have originated from deposits laid down around 54 million years ago and is called puddingstone because the flints resemble the plums in a Christmas pudding.

Between Sunday, April 3 and Thursday, April 14 around 24 of the rocks were taken from the museum’s garden in Hatfield Road.

Most of these came from the site of the Seventh-day Adventist Church during the late 1970s.

The incident is being treated as heritage crime – an offence which harms heritage assets.

PC Sean Lannon said: “Hertfordshire Puddingstone is several millions of years and one of the world’s rarest rocks.

“It is part of our county’s heritage so we are doing all we can to ensure that these stones are returned to the museum.

“I am appealing to anyone who may have seen anyone acting suspiciously in the area between the times stated to please get in touch.

“I’d also like to hear from anyone who may have been offered the rocks for sale or anyone who feels they might know who is responsible for this crime.”

Anyone with information is asked to contact PC Lannon via 101.