克拉的祕密·重量為什麼能決定價值The Secret of the Carat: Why Weight Profoundly Influences a Diamond’s Value
The World of Gemstones · Diamond SeriesThe Secret of the Carat: Why Weight Profoundly Influences a Diamond’s Value
The World of Gemstones · Diamond Series克拉的祕密·重量為什麼能決定價值
寶石世界·鑽石篇

Of the 4Cs, the carat is often the easiest to understand—and also the easiest to misunderstand.

When people talk about diamonds, one of the questions they ask most frequently is, “How many carats is it?” This number may appear simple, yet it has a profound influence on a diamond’s price and standing. But if carat is understood merely as “size,” its true meaning will be overlooked.

From a gemological perspective, the carat is actually a unit of weight, not a unit of physical dimensions. One carat is equal to 0.2 grams, or 200 milligrams, and can be divided into 100 points.

The name “carat” is generally believed to have originated from the carob seeds used by ancient gemstone merchants when weighing precious stones. These seeds were readily available and could be selected for use as counterweights on a balance, gradually becoming associated with gemstone weight. In 1907, the metric carat was officially adopted internationally, establishing one carat as equal to 200 milligrams and thereby creating a uniform standard for gemstone weight throughout the world.

Weight, however, is not the same as apparent size. A deeply cut diamond may appear smaller than the dimensions normally associated with its actual carat weight, while a shallowly cut diamond may look larger when viewed face-up. In other words, carat indicates a diamond’s weight, not the surface area it appears to occupy when viewed from above.

According to gemological principles, the price of a diamond is closely related to its rarity, and carat weight is one of the important factors influencing that rarity.

Small diamonds are relatively common in nature, but as weight increases, diamonds possessing comparable color, clarity, and overall quality become increasingly scarce. The larger the diamond, the lower the probability that it will possess gem-quality characteristics and remain intact. Because of this scarcity, diamond prices do not increase linearly with weight, but often rise at an accelerating rate.

Of the 4Cs, the carat is often the easiest to understand—and also the easiest to misunderstand.

When people talk about diamonds, one of the questions they ask most frequently is, “How many carats is it?” This number may appear simple, yet it has a profound influence on a diamond’s price and standing. But if carat is understood merely as “size,” its true meaning will be overlooked.

From a gemological perspective, the carat is actually a unit of weight, not a unit of physical dimensions. One carat is equal to 0.2 grams, or 200 milligrams, and can be divided into 100 points.

The name “carat” is generally believed to have originated from the carob seeds used by ancient gemstone merchants when weighing precious stones. These seeds were readily available and could be selected for use as counterweights on a balance, gradually becoming associated with gemstone weight. In 1907, the metric carat was officially adopted internationally, establishing one carat as equal to 200 milligrams and thereby creating a uniform standard for gemstone weight throughout the world.

Weight, however, is not the same as apparent size. A deeply cut diamond may appear smaller than the dimensions normally associated with its actual carat weight, while a shallowly cut diamond may look larger when viewed face-up. In other words, carat indicates a diamond’s weight, not the surface area it appears to occupy when viewed from above.

According to gemological principles, the price of a diamond is closely related to its rarity, and carat weight is one of the important factors influencing that rarity.

Small diamonds are relatively common in nature, but as weight increases, diamonds possessing comparable color, clarity, and overall quality become increasingly scarce. The larger the diamond, the lower the probability that it will possess gem-quality characteristics and remain intact. Because of this scarcity, diamond prices do not increase linearly with weight, but often rise at an accelerating rate.

In other words, when color, clarity, cut, and other conditions are approximately equal, a two-carat diamond will often cost not merely twice as much as a one-carat diamond, but several times as much.

This is because a diamond’s price is not calculated solely according to its total weight; it is also influenced by its price per carat. When a diamond enters a rarer weight range, its price per carat may also rise. The increase in total weight and the increase in price per carat therefore work together to drive up the price of the entire diamond.

Diamonds are normally weighed on precision electronic balances. Under GIA rules, the weight recorded on a diamond grading report is expressed to two decimal places, but a stricter method than ordinary mathematical rounding is used: the second decimal place is rounded upward only when the third decimal digit is 9. For example, a diamond weighing 1.768 carats is recorded as 1.76 carats, while one weighing 1.769 carats is recorded as 1.77 carats.

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This precise method of measurement and standardized system of recording make comparisons among diamonds more objective, while also preventing extremely small differences in weight from being improperly magnified.

At the same time, the diamond market recognizes certain special thresholds known as “key weights,” including 0.50, 0.75, 1.00, 1.50, and 2.00 carats. When a diamond reaches or crosses one of these market-sensitive weight points, its price per carat may rise noticeably. This is related not only to rarity, but also to consumer preferences and market psychology.

For example, there is almost no visible difference between a 0.99-carat diamond and a 1.00-carat diamond, yet there may be a noticeable difference in price. This phenomenon reflects the influence of numbers and market psychology upon judgments of value.

From a geological perspective, the scarcity of large diamonds is closely related to the conditions under which they form and are preserved. The formation of a large diamond crystal requires the proper interaction of many factors, including a source of carbon, pressure, temperature, and a suitable growth medium. Once formed, it must also survive a long geological history and remain relatively intact during volcanic magma transport, mining, and processing.

At every one of these stages, a diamond may be fractured, resorbed, or otherwise damaged, substantially reducing its final weight. A large diamond that reaches human hands in a relatively intact state is therefore the result of many conditions working together, which naturally makes such diamonds exceedingly rare.

Throughout history, many celebrated diamonds have become renowned for their astonishing weight. One example is the Cullinan Diamond, which we discussed previously. In its rough form, it weighed 3,106.75 carats and remains the largest gem-quality rough diamond ever discovered. Its discovery not only astonished the world, but also gave people a far more vivid understanding of the rarity of large diamonds.

In a future article, we will examine in detail how the Cullinan Diamond was cut into a number of finished diamonds and how those stones came to be distributed among the jewels of the British Royal Family.

Returning to the practical matter of choosing a diamond, however, one question deserves consideration: Is a larger carat weight necessarily better?

From both gemological and practical perspectives, the answer is not absolute. A diamond with a lower carat weight but excellent cut, color, and clarity will often produce a more impressive overall visual effect than a heavier diamond of lower quality in the other factors.

This also demonstrates that the 4Cs jointly influence a diamond’s quality, appearance, and price. No complete judgment can be made on the basis of any single factor alone.

Perhaps we can understand it this way: Carat represents the “weight of a diamond’s presence,” but whether that diamond is truly beautiful and captivating depends upon the harmonious contribution of other factors as well.

When we look only at weight, we see a number; when we consider all the factors together, we see a complete and genuine gemstone.

(To be continued)