The Quartz Flask is an artifact in Heretic and Hexen. It looks like a clear jar full of purple liquid. Using a Quartz Flask restores 25 points of health to the player. The difference from Doom's medikit is that it may be carried around until needed.
On the lowest skill level, Quartz Flasks will be used automatically if the player is about to die. On all other skill levels, they must be used manually.