We all know that diamond weight is measured in carats. But what is this unusual word and where does it come from? Well, believe it or not, originally this was a Greek word, keration, meaning “fruit of the carob tree”.
This found its way into Arabic as kirat, and into Italian as carato. Hence the English word carat. The original, keration, was a unit of weight based on carob seeds, because it was believed (mistakenly, as it turns out) that carob seeds, which are pretty similar to one another in appearance, had a similar weight to one another as well.
Presumably because adding carob seeds one by one to a weighing scales would give a pretty precise measure on the other side of the scales, so would allow for a fine-tuned measurement, this became a unit of measurement originally for gold. In the 16th century it became used for diamonds too.
But, of course, one person’s carob seed isn’t another person’s carob seed! So there needed to be some internationally recognised standard for diamond weight. In the late 19th and early 20th century, this was achieved, with agreement that one carat was to be exactly 200 milligrams, meaning that a five-carat diamond would weigh exactly one gram.
Hang on, does this mean diamonds can be one of my “five a day”…?!