Yes, this is exactly what I had in mind. I'd tone down the cracks a bit though. It does now very much look like the firestone items. Your first texture really looked cooler, but for the sake of easy identification I think this reddish material is better for the gameplay. If you want to experiment a bit with the texture, I have another idea: Take the sulphur texture, make it red and make the lava-like fluid shine through where now in the sulphur texture there are just black holes (as if the "crust" at those points is very thin). And/or mix it with your current one.

In any case, you should keep the graphic always as a GIMP/PS image because later we will want to e.g. put the cracks/holes into a normal map so we always need the source.

The next step after we found a final texture is to check if my described behaviour is even possible without engine changes and otherwise see how we can get that implemented and/or change the design. Also, I'm not quite happy with my design since other than with the pickaxe it's kinda difficult to obtain this material (incinerate it, let it drop into water) which does make the pickaxe even stronger. Additionally, I was asking myself the other day if the material obtained should be really firestone -> a resource which can be used as explosive immediately and not perhaps some explosive juice (skipping the step with the water). Anyway, I have no time to check out the possibilities in the next 1-2 weeks or so, perhaps you would like to check/think about that?

The question is also if we keep sulphur alongside this material or not.

I wonder, what is the last status of this? How far did you test it, do you have the texture still lying around somewhere?