Glowstone

Glowstone, only mentioned in an extra page at the end of Chapter 01, is a mineral found in the Abyss.

Description
When certain frequencies are applied to a polished Glowstone, it will produce light. It doesn't produce heat, making it an ideal light source. However, when under pressure, it will explode easily.

Uses
Glowstones are used for Delvers' Headlamps in combination of the gem itself, an iron can, an airtight glass container, a wire, a processed talon crystal, and some water.

Due to easily exploding under pressure, they can also be processed into explosives.

Trivia

 * During their fight with Bondrewd, Reg throws a Glowstone Bomb to his arm at close range.
 * The Seeker Camp is equipped with Glowstone lanterns which can be set to emit a high output if a lot of luminance is needed.
 * Glowstones processed into lanterns are the main lightsource while delving, and consist of a mineral that can only be mine in the Abyss. It glows when a constant vibration is applied, and is a dangerous item that explodes when subjected to a large impact or pressure. Buildings are very close together, so open flames are not used. Relics that generate heat are instead used for cooking.
 * Some of the minerals harvested in the Abyss differ depending on the depth of the layer they were mined in. Depth gauges make use of these minerals. Barometers cannot be used in the Abyss because of the force field. Within the device, the minerals change slightly to gas or back to solid. Of course, it can also be used to measure the depth in places other than the Abyss. The gauge used by Riko and Reg, which can measure quite deep, is a rare version of this. It's usually used by Black Whistles.