Shiny Hexagonal Rocks?

You will, eventually, be able to mine those using miners BUT you need to unlock the capabilities first. So the reason your guys are turning around is because they are not yet capable of mining the blobs. The last thing you want to do is have space around the blobs, since they might instead build a mine there, to give you ore and ignore the blobs.

I've just checked on my droid, and the mine gems card is unlocked at 12 mines.

That's the basic steps, though I have seen my followers act oddly in droid, by that I mean they as you describe go to a leash point then come back immediately. When that happens if I leash them again they seem to do what I wanted them to do the first time!
Oh btw use one miner per blobs seam otherwise they all get a bit of gem, and you get a grand total of zero gems. Better to have one do it all in a single seam and let him potentially get half a dozen rather than have a handful of miners get some/none.

Seam lengths vary and their number in relation to the temples. In my current droid game I've dug out the temple nw of starting point, and have started to get the miners employed to start the gems. I had two seams which relate to that one temple one from the beach the other from the hills. I seem to recall there is another temple and seam close by too.
Some gems are not actually mine-able, at least with current capabilies.
In my PC game where I've all current temples uncovered I've a load of blobs I cannot get to since the temple is on top of them, so I need to move something though currently for me in PC game the recently added move object power does nothing so...