Witherite armors, tools and items don't burns in lava, but witherite block and witherite ore burns in lava due to a fault.
Witherite Ore
From the darkness of nether witherite ore is mined below the y: 30 level in nether size and very rare ore.
Witherite Armor
From the darkness of nether witherite armors is provides night vision and fire resistance effect.
Witherite Tools & Items
From the darkness of nether witherite tools & items is gives wither effect to the attacked entity and the spirit of beings killed with the witherite tool gives the user some effects in some probabilities.
Wither Bone & Wither Powder
Wither bone falls from wither skeletons and wither powder can be made with this bone. wither powder is used to make witherite ingots.
