Glowstone

Glowstones are a transparent block that only appears in The Nether, and which gives off a light level of 15.

Obtaining
When broken with any tool not enchanted with Silk Touch, a Glowstone block drops 2-4 Glowstone Dust, or more with a Fortune tool (but never more than 4).

Natural generation


Glowstone only occurs naturally in the Nether, where it generates in coral-like clusters on the undersides of Netherrack.

Trading
Villager clerics will sell 1-3 glowstone for an emerald as a third tier trade.

Light source
Glowstone blocks emit a light level of 15, the brightest possible light level in the game. They are equal to Sea Lanterns, Jack o'Lanterns, Redstone Lamps and beacons with the light they emit.

In redstone circuits
When placing redstone on a glowstone block, being a transparent block, signals can pass from one block to another diagonally. Redstone wire, even though it may appear to connect up the side of a glowstone block and to the wire portion on top, will not send a redstone signal down the glowstone block. This makes glowstone effective for vertical diodes, logic gate designs and space-efficient instant vertical redstone.

Note that upside-down slabs can be used for the same purpose, and are easier to obtain.

Trivia

 * Since glowstone blocks become block entities when moved by pistons, this momentarily stops them from giving off light.
 * Rarely, glowstone can be found touching the ground if the ceiling it was generated on was extremely low (2-3 blocks of clearance).
 * When glowstone is placed 9 or more blocks above ground level (out of its lighting range), the glowstone will actually cast a shadow, despite it being a light-emitting block.
 * When you break glowstone, it has the same sound effect as breaking glass.

Gallery
Glowstone Piedra luminosa Pierre lumineuse (bloc) Izzókő グロウストーン 발광석 Gloeisteen Jasnogłaz Светящийся камень 萤石块