Platinum can be found in native form beyond the chasm. Platinum nuggets may be processed into bars at a smelter. Platinum is the most valuable of all metals (adamantine notwithstanding), and can be used to make furniture, crafts, and coins.
Platinum statues are the most valuable furniture that can be produced in quantity, and can be used to dramatically increase the value of any room, or traded for goods, or just produced to increase the overall wealth of your fortress. Depending on the quality of the craftsdwarfship, platinum statues can range in value from 1,000☼ to 12,000☼.
Despite being only 33% more valuable than gold, platinum coins are worth twice as much as gold coins. A simple explanation for this would be that the platinum coins are 66% bigger than gold coins.