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weight carat

The unit used to weigh gemstones, especially diamonds, is the carat.

Gemstones used in jewelry, due to their high value, are usually small in size and weight. For example, a small round-cut diamond with a diameter of 2 mm weighs 0.006 grams, measured with a highly accurate scale.

You might wonder why this unit is used instead of another from the decimal metric system.

Today, we have highly accurate scales at a very reasonable price. But when these scales did not exist, a way had to be devised to know the weight of gemstones accurately. And this is where the unit of weight called carat came into play.

The origin of the carat, traveling through history

In the 16th century, ships on the Silk Road and from the newly "discovered" America, among fabrics and spices, brought natural pearls from Asia, emeralds from Colombia, rubies from Sri Lanka, etc. In trade, sacks of food, whole animals, firewood, etc., were already weighed with scales, but how could a handful of pearls be weighed accurately? The precision of those scales was not as it is today, but in an international market, those pearls had to weigh the same in Lebanon, Cartagena de Indias, Japan, or Rome...

The incredible accuracy of the carob tree as the origin of the carat

The solution was found in the cradle of commerce, on the shores of the Mediterranean: The carob tree, an ancient tree revered by ancient Indo-European civilizations, has seeds with a shape and weight prodigiously constant: 0.2 grams each. An incredible property that ancient peoples already used. In fact, the terms gram and kilogram were internationally coined much later, in 1889.

The exact origin is uncertain, but it is known that in the trade of pearls and gemstones, carob seeds were used as counterweights on a scale. Whether in Rome or Alexandria, the weight was the same, and it would be centuries later when that standard weight was normalized to 0.2 grams, giving it the name carat.

The term "carob" comes from the Arabic "Al kharoubah" and the Hebrew "kharub," and it is considered to be the root of the Arabic word "Al carat," from which the English word "carat" is derived.

Since then, gems have been weighed in carats, a smaller and more convenient unit than the gram. As mentioned at the beginning, a small round-cut diamond of 2 mm usually weighs 0.03 carats (expressed as 0.03 Ct), a more convenient measurement than the equivalent 0.006 grams.

carob seeds

It is important not to confuse the carat as a measure of weight with the carat as a measure of gold purity. In another article, we analyze the differences.

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