The Carob Bean
Source of the carat weight

So why do they weigh gemstones with a unit of measurement called "carats"? Does it have something to do with orange colored veggies? Nope! In ancient times, when such things as grams and ounces, etc., had not yet been invented, some sort of standard had to be set so people could establish a value of a given item.

In the Mediterranean area, there is a tree called a "carob" tree. The carob tree has fruit called carob beans. The long green beans have beans/seeds inside; all are nearly identical in size. As ancient traders traveled around the Mediterranean and surrounding areas, they turned to the carob bean as a unit of measurement. A gemstone would be weighed and put onto a balance scale... the other side would have carob seeds/beans on it. A stone that balanced out evenly against 5 seeds was said to weigh 5 seeds - then 5 carobs - then 5 carats.

In 1871, the British were establishing what we now know as The Old English Weights and Measures. They found that a carob seed from one side of the Mediterranean weighed 0.1885 grams and from the other side weighed 0.215 grams. Over time, between 1878 and 1889, these two numbers were averaged, and the number 0.204304 was used. Subsequently, several trees had all of the beans stripped from them, counted and weighed... the average weight was 0.197 grams. This figure is used today; carats are figured as 5 per gram... or 200 milligrams.

Carob Bean Pod
Carob Tree with Bean Pods

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