Rock Zone

Rock Zone is an unused zone that would have been in Sonic & Knuckles. It's not to be confused with Rock World Zone, which was set to appear in Sonic the Hedgehog 2. The only proof of this zone's existence is a supposed magazine scan of the zone, with no trace of the level in the final game. It appears to have been scrapped very early in development, possibly being replaced with Lava Reef Zone judging by how similar they are.

Contents
Rock Zone appears to use the same rocky tileset as Lava Reef Zone, albeit more brown. The only known part of the level is seen in the screenshot of Rock Zone. It appears to be a simple level with no background, implying it was either a test level or a very early level. The screenshot itself shows a flat plane with a ramp upwards onto higher ground, as well as what appears to be a ceiling above the ramp area.

Existence
User Juanton510 attempted to create a page for Rock Zone on the Sonic News Network, attempting to spread the news about Rock Zone to no avail. This same user also created the page for Dust Hill Zone, a zone originally intended for Sonic 2.