Question

what is the most valuable gemstone on the planet, in terms of weight?
diamond
emerald
sapphire
ruby

Explanation:

Among the listed gemstones, rubies (especially high-quality, untreated specimens) have a higher per-unit-weight value than diamonds, emeralds, and sapphires. Rarity, color saturation, and demand drive this higher value per carat/gram.

Answer:

ruby