Has anyone tried using stone (or rock) wool in place of vermiculite? I just got a sample and am eager to try it in a small area.

I read that stone wool has been used as building insulation in Europe, but is also being formed in blocks for seed starting and hydroponics. It is made from superheated basalt and chalk, and is touted to be an environmentally friendly, sustainable product.

This stuff is very absorbent, but I have no idea how its structure will hold up in soil over time--it seems to compress with pressure and sort of falls apart if handled when wet. Not sure whether it will be cost effective, either.