A couple issues I'm noticing with these:
The depressions themselves are movable, Despite the book saying quart left, obsidian right, the obsidian seems to work (with purple flash animation) and create the bridge on the left, while the one on the right doesn't seem to do anything. Placing the quartz on either side doesn't seem to stop the altar from zapping you. They also seem to stack oddly.
Not a game stopped (once I realized placing the obsidian on the left worked), but just wanted to throw it out there.