Polish border guards seized 130 kilograms (287 pounds) of amber from Russia last year, four times as much as in 2012.

“Attempts to smuggle amber from Kaliningrad have intensified significantly. According to statistics, nationals of Russia, Poland and Lithuania are making money on this,” a spokesman for the Polish cultural center in the Russian Baltic exclave of Kaliningrad said, citing data obtained from a Polish customs department.

“A total of 30 kilograms [66 pounds] of amber were seized on the border in 2012, compared with 130 kilograms last year,” the spokesman said.

In a first major seizure this year, Polish border guards found 30.5 kilograms (67 pounds) of amber in a fuel tank of a car driven by a Russian national.

Experts estimate that 60-100 metric tons of amber is illegally mined every year in the Kaliningrad Region. The area is believed to hold over 80 percent of the world’s total known amber reserves and is home to the world’s only strip-mined natural amber deposit.