Gemspark Blocks

Gemspark Blocks are blocks that glow in low light only. The color of the glow depends on the gem used to craft the block. They are also mechanisms, as their glow can be toggled by wiring them to a trigger (though wiring them cannot force their glow to show up in higher light levels, and low light will still be required). Gemspark Blocks are crafted from Gems and Glass at a Work Bench.

Trivia
It is possible that these items were taken from a TConfig Mod by Yoraiz0r (one of Re-Logic's programmers, and former Modder) holo the everything along with several other items and mechanics.