For an idea of their HPs, I randomly killed 10 of these from all over the zone. One on one, strictly melee damage, went as follows:
1 - 322
2 - 307
3 - 286
4 - 314
5 - 322
6 - 315
7 - 251
8 - 287
9 - 308
10 - 311
So they have on average 300 HPs, give or take about 50 depending upon level, I assume.

Block of Clay
Muddite Mud
Silver Bar
Silvril Ore