Obsidian should be fair game, IMHO...as should be things like fulgarite (sand fused by lightning) or leftovers from meteor strikes.
Lets see...
- Virtually unbreakable potion flasks
- Virtually unbreakable lenses (glasses, spyglasses, etc.)
- Virtually unbreakable windows
- Arms & armor not susceptible to rusting, most acids, heat metal spells...and extremely fashionable, to boot.
- Arms & armor that are difficult to see in wet/snowy/icy conditions (ever find glasssteel caltrops in the river with your feet?)
- Shields that let you maintain LoS
- Expands the list of arms & armor usable by Druids
Skaldril's Scintilating Scales
This is a suit of scale mail constructed entirely of glass scales tempered by the magic of glassteel. Each scale has been crafted to look like the tip of a peacock's feather, so the entire suit is a riot of color.
However, beyond the stylish protection the suit offers, it also grants a +2 to Diplomacy checks, and allows the wearer to cast Hypnotic Pattern 5/day as if he were a 6th level Sorcerer, using the wearer's Charisma score as the casting stat.
Special: Battle Sorcerers and Bards treat this armor as if it were light armor.