Traumatic optic neuropathy (TON) refers to an acute injury of the optic nerve secondary to trauma. The optic nerve axons may be damaged either directly or indirectly and the visual loss may be partial or complete.
In Minecraft, emerald ore is very hard to find and is found in small deposits in the Extreme Hills biome. You can usually find emerald ore between 13 and 31 blocks below the ground and close to lava. So if you see a pool of lava in the Extreme Hills biome, that is a great place to start mining downward.
Emeralds are green for the same reason as rubies are red. The ruby is a regular crystal of corundum containing chromium as an impurity. The emerald is a regular crystal of beryl that also contains chromium as an impurity. Beryl is the term given to beryllium aluminum silicate (Be2Al2Si6Ol8). In rubies an aluminum atom in the beryl lattice is replaced by a chromium atom.