Where can you find a platinum ore in dragon quest 9?

You get it in the Uruban Marshlands keep on going south...then you find this giant random crystal gaurded by Poisonious Watse use Safe Passege getting to it unharmed.

Then if you see a twinkling spot right next to the giant mythril cryastal press A right next to it then you get your mythril ore. They may be two or three or even one. You can sell it for 3000 gold coins if you sell it at Bloomingdale or another town cheaper then that!

If you sell it like at Gleeba or Swindimples Academy it would only be 300 if you sold it there.