Which gem is the most expensive?

Ah, that's quite an intriguing question indeed! When it comes to gems, the most expensive one is quite a subjective matter, as the value of a gemstone can be influenced by various factors such as rarity, quality, demand, and even the sentimental value attached to it. However, if we're looking at purely monetary terms, diamonds are often considered to be among the most valuable gemstones. In particular, the rarest and most sought-after diamonds, such as those with exceptional clarity, color, and cut, can fetch astronomical prices at auctions and private sales. But let's not forget about other precious gems like rubies, sapphires, and emeralds, which can also be incredibly valuable depending on their unique characteristics and rarity. So, the answer to your question really depends on the specific gemstone in question and the criteria being used to determine its value.