The "Minecraft Caves & Cliffs" update is scheduled for early 2021, but ahead of that milestone, Mojang has released the first snapshot showcasing the new content.Minecraft snapshots are basically a Java version of the game. only accessible in the testing phase.

The snapshot does not appear to affect cave creation, nor do the new biomes Lush and Dripstone. However, there are plenty of new things to see and try, the most exciting of which is definitely the new Amethyst Block. Not only do they look pretty (the amethyst block is pictured above), but they also make "beautiful sounds" when touched, so expect some clever music-making from some of Minecraft's most dedicated players.

Also in the snapshot is a bundle, "an item that holds other items," according to Mojang. Other items include candles in 16 colors, a cauldron that can hold lava, a peek-a-boo window for viewing the view, and colored glass.

Snapshot 20W45A is quite generous in its approach to new content, and in addition to all the new materials, changes have been made to existing ones. For example, minecarts now work underwater (hooray).

A complete and lengthy overview of the snapshot can be found here; for other information you need to know about the Caves & Cliffs update.