They cant both be volcanic glass. And we already know that Glass is effectivly Obsidion, so what does that make Ebony?
Last I checked, Ebony armor was metalic, not amorphous
Sure they can, rubies and diamonds are different kinds of gemstones too, arent they?
'Glass' has obsidian like qualities, but it has different properties from obsidian. It appears to be more viscous and have greater structural strength, it can be molded and does not shatter when impacted.
Lore-wise, 'ebony' is a volcanic glass with magical properties. It is just called 'ebony' because of the mystical undertones of that word, same with 'glass'.
Who knows what processes are used, how much metal and leather actually holds the ebony plates together, or its exact properties.
I tend to think of it as a space-age ceramic only naturally occuring.