Glassrock

Some areas of the Deep have rock surfaces which seem to have been molten, by some mammoth magical or elemental forces, into irregular, glassy surfaces. These are extremely slippery and difficult to traverse safely. The only safe movement rate through such areas is at one-quarter normal speed. Any attempt to move faster requires a Dexterity check for every step to avoid falling down. PCs who fall slip and slither d6+6x10 feet along a passageway until they come to rest against a wall. There is a 15% chance that this slip means the PC bangs his or her head against a passage wall (unless protected by a helmet) and is Stunned for d4 rounds thereafter. A fallen character can only regain his or her feet by rolling less than half his or her Dexterity on d20. Mounts will flatly refuse to traverse glassrock.

Note that a Shatter spell cast into an area of glassrock has a 50% chance of causing a radiating effect through the whole area, so that a distance of d4x100 yards of passageway becomes filled with broken and scrunched glass that is safe to walk on at normal movement rates. However, if this does not occur then the spell may (20%) make things worse, not better, breaking the glassy rock into sharp, jagged fragments that act exactly like Razor Rock.