That is bogus information. Both are corundum Al 2 O 3 . But since everyone says so, it's ok to use it in a sales pitch. Emeralds can be both red and green. Emeralds are green only.
Emeralds are green only.
Yes, due to interlocking crystal structure, they are more difficult to break. No, There are no gemstones that are tougher than diamonds. No, Cubic zirconia is toughter, but jadeite is not. Due to its interlocking crystal structure, jadeite splinters relatively easily.