Amethyst Gemspark Block

Gemspark blocks glow on their own in the color of the gem that made them, which lets you light a room from its walls and floor instead of hanging torches everywhere. The purple cast from the amethyst version is one of the dimmer, moodier options in the set. They glow while sitting on the ground as dropped items too, so a stack you have not picked up yet lights the tunnel.

One catch that trips people building glowing houses: housing validation does not count them. A room walled entirely in gemspark still reads as unlit and no NPC will move in until you add a real light source.

The game files these as mechanisms, not just blocks. Run wire to them and a switch or timer turns the glow off and back on, which is the foundation of every animated sign, marquee and pixel art display people build with them. The unlit state still occupies the tile, so nothing shifts when it toggles.

Running an Actuator over one does not put the light out either. An actuated gemspark keeps shining while you walk straight through it, which is handy for hidden doorways that stay lit.

Water falling through a lit gemspark block picks up its color and holds it for the entire drop, glowing the whole way down and throwing faint light onto nearby surfaces. It is the cheapest way to make a decorative fall look deliberate. Two falls in different colors that meet will blend where they touch. Lava, honey and shimmer ignore the effect completely.

The one that catches builders out is the half block case. A vertical fall supported only by a half block keeps its plain color even when that half block is gemspark, so thin ornamental streams need a full block in the path somewhere.

Amethyst takes paint normally. The diamond variant is the exception in the family: only deep paints change its base color at all, and the result comes out lighter than every other gemspark given the same deep paint. If you are matching colors across a build, paint the diamond pieces last.

As a curiosity, the sapphire variant is generated during world creation and then cleaned up before you ever see it. Occasionally one survives underneath a chest or a life crystal, which is why an untouched world will very rarely have a stray glowing block buried in it.