What an emerald actually is.
Those two elements, chromium and vanadium, are the whole story of the colour. Where a stone also carries very little iron, the green stays pure and warm rather than tipping toward grey or blue; that combination is uncommon, which is part of why fine emerald is rarer than most people assume. Not every green beryl earns the name: the trade reserves “emerald” for material with enough depth of colour to read as unmistakably green and lighter or paler beryl is sold under other names.
An emerald sits at roughly 7.5 to 8 on the Mohs scale of hardness, so it resists scratching well. Toughness, resistance to chipping and breaking, is a different matter: most emeralds carry internal fractures from the violent conditions in which they formed, which makes them more brittle than a ruby or sapphire and is the single most important fact behind how they are cut, treated and cared for.
