Petroleum products, whose reexport was a top earner in 2002, were the only mineral product that played a significant role in the Seychelles' economy. Mineral production consisted mostly of unspecified quantities of clay, coral, sand, and stone. Although production of guano (a phosphate fertilizer comprising bird droppings, extracted from Assumption) ceased in the mid-1980s, a plant with a capacity of 5,000 tons per year remained; modest production was unofficially reported in the mid-1990s. Experimental granite quarrying in the bedrock of Mahe and nearby islands was tried in the early 1980s. A South African company's efforts to quarry and sell granite in the early 1990s stagnated due to opposition by environmentalists; production of lime and cement from the abundant coral was also considered. Polymetallic nodules were known to occur on the ocean bottom near the Admirante Islands. The Seychelles comprised 40 granitic and at least 50 coralline islands.