Glow Lichen

A glow lichen is a non-solid, light-emitting fungi growth that resembles sparse moss that is $1/16$ of a block thick. It can generate, or be placed, on any side of a solid block.

Natural generation
Glow lichen generates naturally on the sides or bottom of, , , , , , , and s that are exposed to air or water sources at or below Y=56. $$, if the Caves & Cliffs experimental gameplay toggle is enabled, glow lichen can generate up to Y=119. It generates more frequently in ravines. It can be found underwater as well as in oceans.

Post-generation
bone meal causes glow lichen to spread to a random adjacent block if possible, otherwise the bone meal will not be 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, but using shears is the only way to collect it. Enchanting shears with Efficiency provides no additional benefit. Breaking them with an axe is the fastest, but does not allow for collection.

Light
Glow lichen emits a light level of 7. In Bedrock edition it emits a light level of 10.

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. When mined with the correct tool, all glow lichens in the block will drop.

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 fungi species in a symbiotic relationship.