For starters, Rio, which is listed in London and Sydney, already rejected a merger approach from Glencore in August. Yet share price movement for both companies Tuesday, after reports of the approach emerged Monday night, suggests there are some in the market banking on a deal.
On Tuesday, Glencore confirmed that it had made "an informal inquiry by telephone call" in July this year to gauge whether Rio was interested in merging. Rio responded in the negative.
Glencore said it was no longer considering any possible merger with, or offer for the shares of, Rio, on Tuesday.
However, there are a number of obvious overlaps for the two mining companies, including in iron ore and coal production and logistics, which might mean cost savings for a merged entity.
Here we take a look at the key issues which might hobble a merger, which would create a $160 billion company, and the world's largest listed miner.