It is hard to say. 50 lbs is 1/3 the max load limit on the mount, but that doesn't mean it can use 1/2 as many studs and still hold 1/2 or less the weight. I guess some of it will now depend on the thickness of your drywall/mineral board, and what type of anchor you use in the drywall. I would say use at least 1 or 2 3/16" or 1/4" toggle bolts and you should be fine (a 3/16" toggle bolt in 1/2" drywall can safely hold 25-30 lbs, so assuming a worse case scenario, it should be able to hold 1/2 the weight of the TV on just the one bolt).
I do not recommend using plastic expansion anchors or even threaded drywall anchors. There will be too much weight for them. You really need to added strength/stability offered by a toggle or a molly anchor.