Trovants are spherical and slightly irregular-shaped rocks. They can be as small as less than an inch, or a couple of millimeters, in diameter and weigh only a few grams, or they can soar up to 15 feet (4.5 meters) high and weigh several tons. These odd, gravity-defying boulders have baffled observers since the 18th century with many a curious soul suspecting they were dinosaur eggs, plant fossils or even alien pods.
Scientists believed trovants to be a type of concretion — a mound of mineral matter (specifically gritstone and conglomerates) embedded within rock layers of limestone, sandstone or shale. They often form from minerals precipitating, or settling, out of water collected around a nucleus of pebble, leaf, shell, bone or fossil.
However, in 2008, the International Geological Congress in Oslo claimed trovants were incorrectly classified as concretions because there was no mineral difference between the stones and the sandstone beds on which they sat. There was also no distinct nucleus inside them.
Whatever they are, scientists believe that based on their makeup and locale atop the sands, these weird stones are older than man — shaped by earthquakes around 5.3 million years ago, during the Middle Miocene sub-epoch. The surrounding sands also suggest the area was an ancient marine environment, which may explain why bivalve and gastropod fossils can sometimes be found in them.