And how much Pt has ever been mined?

Platinum is even more scarce than gold. Only 3.6 million troy ounces are produced per year. Its specific gravity is 21.45, and it was discovered in the 18th century, not in 3,000 B.C., like gold. If you assume that the world has produced 3.6 million ounces per year for 50 years to estimate the total worldwide supply, all of the platinum in the world would fit in a cube that is 6.3 meters (about 20 feet) on a side. In other words, all of the platinum in the entire world would easily fit in the average home!

Therefore, a trillion dollar coin (at $1593/oz) would require roughly 174 years worth of world Pt production, give or take, and leaning heavily on assumptions.

And yes I know that denomination is not the same as materials cost; just look at our 2 cent penny. And the new $20, which does not contain $20 worth of slick polymer.