Why Gemstones Are Measured in Seeds

Next time you admire a diamond ring, thank the humble carob tree. The carat—that mystical unit that determines whether an engagement ring costs a month's salary or a year's—traces its origins to a small, brown seed used by ancient merchants.

The word "carat" derives from the Greek keration, meaning "carob seed." These seeds had a reputation for being remarkably consistent in weight, making them ideal as counterweights on balance scales.

Nature's Perfect Measuring Tool

Ancient gem traders across the Mediterranean and Middle East faced a problem: they needed a reliable, portable standard for weighing precious stones. Coins varied between regions. Metal weights could be shaved or tampered with. But carob seeds? They were everywhere, and merchants believed each one weighed almost exactly the same.

This belief wasn't entirely accurate—carob seeds actually vary by about 5%—but it was close enough for ancient commerce. The seeds became the go-to standard for gem trading from Greece to India.

From Seed to Standard

For centuries, the carat remained frustratingly inconsistent. Different trading centers used slightly different carob seeds, leading to regional variations:

• The Florentine carat weighed about 197 mg
• The Arabian carat came in around 204 mg
• London's carat hovered near 205 mg

This chaos persisted until 1907, when the metric carat was internationally standardized at exactly 200 milligrams—roughly the average weight of a carob seed. The Fourth General Conference on Weights and Measures made it official, and the gem world finally had consistency.

Why 200 Milligrams Matters

That standardization transformed the diamond industry. A one-carat diamond weighs precisely 0.2 grams, no matter where in the world you buy it. The system divides neatly into 100 "points," so a half-carat stone is 50 points, making pricing calculations straightforward.

The carob tree (Ceratonia siliqua) still grows across the Mediterranean, its pods hanging heavy with seeds that changed how humanity values its most treasured gems. Those ancient traders couldn't have known they were establishing a measurement system that would endure for millennia.

Modern gemologists use precision scales accurate to thousandths of a carat. Yet every time they weigh a diamond, they're participating in a tradition that began with merchants pulling seeds from their pockets to balance against rubies and sapphires in a dusty marketplace.

The carob tree gave us more than just a unit of measurement—it gave us carob powder, a chocolate substitute, and locust bean gum, a common food thickener. But its most lasting legacy remains invisible in every jewelry store: the idea that something as ordinary as a seed could become the standard for measuring extraordinary beauty.