So today I did an experiment.
I was going to Rimmington mine to get ores for bronze bars for summoning when I saw a level 3 crashed star. I got the full rewards, one of which includes a 15-minute mining boost, enabling you to mine an extra ore.
I went to Falador mine and started mining random stuff. My usual mining gear consists of at least Varrock armour (1 additional ore) and a Glory amulet (greater chance of mining gems).
Well, the star reward and Varrock armour teamed up, and I got 3 coal ore at once! If I had gotten a gem, too, that would have been awesome.
Now, if I could get the external client to not die every few minutes, I'll go back to summoning.