The cost of a diamond is primarily determined by its carat weight, cut, color, and clarity (the Four Cs), along with additional factors like rarity and demand. Among the Four Cs, the cut of a diamond can significantly impact its price, but there is no one “most expensive” cut for diamonds. Instead, the price of a diamond depends on the overall quality and rarity of the specific stone, regardless of its cut shape.

Round brilliant-cut diamonds are generally the most expensive per carat because of their exceptional light performance and popularity. Their precise faceting and symmetrical design maximize brilliance and sparkle.

Other fancy diamond shapes, such as oval, emerald, marquise, and pear, can also command high prices if they exhibit exceptional cut quality, are well-proportioned, and possess desirable characteristics in terms of color and clarity. However, within each shape category, prices can vary widely based on the specific qualities of individual diamonds.

Ultimately, the most expensive diamond is one that possesses the highest combination of the Four Cs, along with any unique features that make it rare and desirable. It’s essential to evaluate diamonds on a case-by-case basis and consider all aspects of quality when assessing their value.