Spectrolite, Ylamaa

Spectrolite is Finland's national gemstone, and it comes from one place: Ylämaa, a former municipality in South Karelia, in the far south-east of the country, merged into Lappeenranta in 2010. The stone is an uncommon variety of labradorite, a calcium-rich feldspar first identified in Labrador, Canada, and named for it. Most labradorite flashes in tones of blue, grey and green. Spectrolite shows a far richer play of colour, blues and greens joined by orange, pink and purple, so distinctive that the name became a brand for stone mined only here.

The fire is a trick of structure, not pigment. In plagioclase of the right composition, cooled very slowly, the crystal separates into microscopic layers, and when their spacing falls between about 128 and 252 nanometres they reflect light back in interfering colours that shift as the stone turns. In rock that cooled too fast the layers never form, and plenty of labradorite stays dull.

The deposit was found by accident in a war. The Finnish geologist Aarne Laitakari had described spectrolite and spent years searching for its source when his son Pekka struck it at Ylämaa in 1940, while building the Salpa Line fortifications there. Quarrying began after the Second World War and grew into a real local industry. In 1973 the first workshop in Ylämaa began cutting and polishing spectrolite for jewellery, and a gem centre followed, with training for gem cutters and an annual Gem and Mineral Show started by the mayor, Esko Hämäläinen.

Today Ylämaa's Gem Village holds a gem museum and the country's largest gem and jewellery fair each July. In summer, guided tours leave the museum daily at 12:30, no booking needed, for the spectrolite quarry, where visitors pick up genuine gem-quality spectrolite with their own hands. The same trip takes in one of Finland's largest granite quarries, the source of the famous Baltic Brown and Baltic Green stone, and the old Salpa Line defences can be added on.