Lightstone

Lightstones were yellow, and sometimes blue, glowing crystals that grew in caves and were mined by Matoran, specifically Onu-Matoran. They were used for lighting up dark places, most notably the tunnels of Onu-Koro, Onu-Wahi, and Onu-Metru.

One time on Mata Nui, the Lightstone mine was cut off from the workers by an unsuspectected lava breech, thus causing Onu-Koro work to come to a slow crawl because no one could see. Oil lamps were instead used during the crisis. Later, the mine was reachable again and work continued.

Valokivi