After buck has gone back into Stark mountain with it you go back in talk to him he leaves you take the magma stone and Heatran apppears (lvl 50).
stark mountain
No
in stark mountain
You can only find a Magma Stone in Pokemon Black 2, White 2, Pokemon Diamond, Pearl, and Platinum. It is not available in Pokemon Black and White.
You don't get the magna stone from buck in Pokemon platinum.
It does not evolve with a dusk stone in Pokemon Platinum
You can catch Heatran in stark mountain. You end up defeating team galactic and you lead buck to the magma stone. Heatran will appear after you speak with buck in the back of stark mountain. I think your thinking of Diamond or Pearl, I tried it in Platinum. Doesn't work.
there is no bronze stone
Visit stark mountain a second time and you should battle heatran and keep the stone. I do not know completely because I have platinum
a grass Pokemon
The Pokemon that can use oval stone in Pokemon platinum is Happiny. It is the pre evolve form of chansey. Mostly every chansy you catch have a oval stone.
get heatran