Thanks for your question! This backspash is glass.
I used a combination of an opalescent tile in varying sizes (Casa Dolce Casa, Neutra Vetro Glass Tile, Color: 03 Avorio Lux) with randomly inserted glossy glass tiles in the gray (Walker Zanger Spa Glass, Serenity Gloss Splash Liner). I used that to tie in the soapstone counters and get some added detail in the splash without it getting too busy.

Hi! Question: avorio lux is color no.2, and silver is color no.3, so is it silver or avorio? Ps I love them both :)

That tile looks fantastic. It looks like a longer version of this http://www.glasstilestore.com/collection/pearl-shell-tiles/south-sea-pearls-mini-brick-pattern-tile.html

I really like this tile-granite-wood combo. I have very similarly stained cabinets and floor and dark granite (Volga Blue that reads mostly as black w/silver & green). I've had a heck of a time finding a backsplash that ties the warms and cools together without making the kitchen look even darker… this could be the solution! Are you familiar w/Volga Blue? Do you think this backsplash would work? Also, what is your paint color? It's really lovely with everything else. Thanks so much!