Orebfuscation

Orebfuscation (from ore and obfuscation) is a common mechanic on civ servers which makes sought-after blocks (such as diamond ore) appear visually as undesirable blocks (such as stone) until the player comes within a certain distance. This replacement is purely visual, and is meant to lessen the effectiveness of x-raying (using disallowed mods to see blocks a vanilla client would not be able to).

Orebfuscation is applied by the Orebfuscatorplugin.

Mechanics

Block Hiding

Orebfuscator will render several blocks as stone when viewed from a distance. The blocks hidden in this fashion include valuable blocks like ores, and also blocks which generally indicate defensive infrastructure, civilization, farms, bases, or anything else a player might want to keep hidden.

Blocks generally rendered as stone from a distance include snitches (both noteblocks and jukeboxes), obsidian, chests, ender chests, trapped chests, furnaces, crafting tables, and clay.

When a player comes within a certain radius (varies by server, but usually around 8 blocks) of these blocks, they are rendered as their normal block. Even if the player moves outside of the radius, they will keep their normal appearance until the player unloads the chunk.

Random Blocks

Even with block hiding, there can be tell-tale signs of civilization or defensive infrastructure, such as long dug-out tunnels or a box of (what appears to be) stone. To guard against this, Orebfuscator also fills the world with fake random valuable blocks underneath the surface, to make it more difficult for x-rayers to see through these blocks.

Blocks that are rendered underground in this fashion typically include every kind of ore, air, cobblestone, mossy cobblestone, stone, obsidian, tnt, and clay.

Unless you're x-raying, you should never see these hidden fake blocks. The one exception is if you mine while the server is lagging - sometimes the server can't send you the true value of a block before you break a block next to it and expose it, resulting in the display of random hidden blocks.

Effectiveness

Orebfuscator is generally considered effective against players who x-ray. However, it is not completely effective, as x-ray may still allow players to see nearby blocks that would otherwise be blocked from sight.