Normally, when a geode generates near bedrock, smooth basalt and calcite generate sorrounding the geode, but it generates instead of bedrock when it's very close to y=-64

You can see it if you find a geode near bedrock or you can see it in this seed at this coordinates
5027632123193920988 1650 -67 -1280 Here you can see how smooth basalt and calcite have been generated all across bedrock