Scottish agates

Scotland's agates grew inside old lavas. Along the east coast, basalt and andesite flows of Old Red Sandstone age, about 380 million years old, come down to the sea from near Stonehaven to well south of Dundee and run inland to the south-west, linking with similar lavas in Ayrshire. As the rock weathers, the hard banded nodules fall free, and longshore drift carries them along the beaches. The coast south of Montrose, around Ferryden, Scurdie Ness and the old fishing village of Usan, is the classic ground.

Usan has been collected since at least the 18th century. Its andesite flows run out into the sea, and the stretch of shore to the south is still a prolific source, though the easy stones went long ago. In the late 19th century, the story goes, a hermit lived in a small cottage just above the high-water mark and made his living selling stones to visitors; its ruins still stand. Usan also holds the Blue Hole, once the most famous agate locality in the British Isles. The mineralogist Matthew Forster Heddle worked it hard, reputedly with explosives, and he and others brought out onyx and fortification agates up to about 250 mm across, of a deep inky blue never matched before in Scottish stone. Many are now in the National Museum of Scotland. Collectors still argue over exactly where the Blue Hole was.

Those stones fed a whole trade. "Scotch pebbles" were set into the brooches and ornaments of Scottish pebble jewellery, which Queen Victoria's love of all things Scottish made fashionable. Lapidaries in the back streets of Edinburgh's New Town cut them, buying from collectors who worked Usan, Kinnoull Hill near Perth, the Campsie Hills and Rum, and by one estimate about two thousand people were working gold, silver and agates in Scotland by 1870. Each town had its signature: Montrose was known for blue-grey stones, Kinnoull Hill for reds and whites.

Collecting today comes with rules. NatureScot points out that taking samples is not covered by Scotland's outdoor access rights, so landowner permission is needed before going on a site to remove anything, and taking stones without the consent of whoever owns the mineral rights, usually but not always the landowner, may be regarded as theft. On a protected site, unauthorised collecting can be an offence that Police Scotland treats as wildlife crime.