Basalt. You see it everywhere in the Copper Country. It's the volcanic rock from which the area's namesake ore was extracted, leaving piles of fragments still rich with copper and silver.
So, thought Erik Kiilunen and Ken Keranen—businessmen, engineers, and fiercely loyal residents of the Keweenaw—why not use local basalt to make the rebar that reinforces concrete in roads, bridge decks, and buildings? Basalt fiber-based rebar would be stronger, lighter, and more resistant to alkalinity, which can cause concrete to expand and crack..." Read full article here.