The Onyx is a new gem that was added in the 6.0 update. It can be obtained from mining Onyx Ore in the Mining World, and is the rarest generating ore. The ore always drops 1 Onyx gem. rendering any fortune enchantment useless. Unlike the other gems, Onyx does not stack, meaning you must have plenty of inventory space to collect these gems. When a Gold Rush event is active, Onyx gives the most amount of points, at 5. Presumably due to how rare this ore generates.
At the current time, Onyx tends to sell for 600-2500 coins in Shop Chests.
Is it used in the crafting recipes of; Onyx Rings, Onyx Amulets, Onyx Lamps, Onyx Hanging Lights, Onyx Blocks (Craftable within the Infusement Altar), Brown Dwarf Stars and Spike Blocks. The Onyx Hanging Lights function similarly to a torch but can also be hung on ceilings. Onyx Lamps function the same as any other lamp, requiring a redstone signal. The Onyx Rings and Amulets give the player a chance of triggering a Protection I effect or a Unbreaking I effect respectively. The Brown Dwarf Star is used as fuel for the Infusement Altar and lasts for 500 ticks. Spike Blocks are used as traps and damages entities when they walk over it.