There were two big rocks in the bean field dug up by a big farm cultivator, both about the same size but the round rock I could not pick up but the flat rock I could. Does dolomite have iron in it? Does dolomite have gold in it?
Limestone is made of calcite (calcium carbonate) and dolomite's composition is Ca,Mg carbonate. The are similar in density so you wouldn't really notice the difference if you picked up a chunk of each. No significant Fe or Au in dolomite. The heavy one might be igneous and the other sedimentary.
The tire should be repaired by plug-patch which cannot fall out while going down the road. A regular plug could come out causing rapid deflation which could lead to loss of control. That is why most tire shops stopped using them except on low speed tires like tractors.
I wouldn't leave the nail in the tyre, but neither would I plug it. I'd take it to a tyre fitters, because the tyre should come off to fit a mushroom plug from the inside. They might advise a new tyre anyway for safety.
Dolomite is harder and denser than the calcite form of calcium carbonate or limestone, and is more chemically inert and more impervious to acid attack.
