Glow Lichen

A glow lichen is a non-solid, light-emitting block. It can generate, or be placed, on any side of a solid block.

Natural generation
Glow lichen generates naturally in the interior of caves (at any height) on the surface of stone, andesite, diorite, granite, calcite, tuff, deepslate, and dripstone blocks that are exposed to air or water sources. It can be found underwater, but cannot generate in the deep dark biome.

Post-generation
bone meal causes glow lichen to spread to a random adjacent block if possible, otherwise the bone meal is not consumed. By fertilizing one lichen with bone meal, it is possible to cover the sides and the top of an adjacent block, but not the back. Otherwise, glow lichen does not spread naturally.

Breaking
Glow lichen can be destroyed with anything, most efficiently with an axe. However, using shears is the only way to obtain glow lichen. Enchanting shears with Efficiency II allows for instant mining.

Light
Glow lichen emits a light level of 7.

Placement
Multiple glow lichens can be placed in the area of one solid block, such as covering three sides of a corner. When such glow lichens are mined, all glow lichens occupying the same block are also mined. Mining with shears causes all glow lichens in the block to drop.

Glow lichens cannot be broken by flowing water or lava, similar to signs. Therefore, they may be used to control the flow of these fluids.

Composting
Placing a glow lichen into a composter has a 50% chance of raising the compost level by 1.

Trivia

 * This block was hinted at by Henrik Kniberg, who explained that the glowing ores at Minecraft Live 2020 were prototypes for this.
 * If the player removes all directional states using a debug stick, the block becomes invisible, but the light emission remains, unless another block is placed there.
 * In real life, the lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungus species in a symbiotic relationship.