Wowaddicts Legion

As per wowhead: https://www.wowhead.com/quest=41014/fury-road#comments, the mobs should respawn almost instantly, and they should drop 10x unrefined gems.
At this moment they have a respawn time of about 7-8 minutes, and the drop rate is about 10%.

1. You are looking for mobs that have 5.2 million health. If you can't see these, you're bugged and out of phase. Go out to the guy you got the crystal from and get a new one. This normally clears it.
2. You really don't need to go any further than the first room of the cave - the mobs respawn almost instantly.
3. Most important - when killing mobs and others are there, keep moving! The crystal drops are not personal loot and you pick them up by moving over them. When the crystals appear, there is generally a scramble to get them - first there gets the crystals. Though don't worry, a single mob dying will drop 10+ of these. So even if there are lots of people there, you'll all finish this quest fairly quickly.