Emeralds are graded and valued based on several factors, including their colour, clarity, cut, and carat weight. The colour of an emerald is graded on a scale from light to dark, with the most valuable emeralds being those with a deep, rich green colour. The clarity of an emerald is graded based on the presence or absence of inclusions, with clearer and more valuable emeralds having fewer inclusions. The cut and carat weight of an emerald are also taken into consideration when determining its value.