Have you ever noticed that the word carat has two separate meanings, both of which help describe the quality of high-value investments or luxury items? Although these two uses for the word are related (as we will see below), they are not the same. Learning the difference between carat (for diamonds) and karat (for gold) can save precious metals investors lots of time, confusion, and money down the road!
Carat: One Word, Two Definitions
In order to distinguish between the two uses, the spelling “carat” denotes gem weight while “karat” expresses gold purity. This convention is generally only followed by the United States, however; around the world, "carat" is used in both cases, creating some degree of confusion.
Carat: Not a Vegetable But a Seed
Our search for the origins of this tricky word will take us back at least 1,700 years, to the ancient Mediterranean.
The proverbial roots of the carat unit lead us back to the Carob tree (binomial nomenclature Ceratonia Siliqua), whose seeds (or beans) were well-known throughout the ancient world to be very uniform in size and weight. This made carob seeds the ideal standard as a measure of weight for valuable commodities--gold, gems, pearls--where a few milligrams meant a lot in trade.
The carob seed was known among the pearl traders of the Persian Gulf as qira? (?????) in Arabic. The Ancient Greeks translated this as kerátion (?e??t???), which in turn became carato to the Italians, which eventually became the English word carat.
The carob tree has been found in abundance across the Mediterranean and Middle East for millennia. As a result, populations across North Africa, Southern Europe, and Central Asia were all familiar with the carob bean, as there were plenty on hand to use as a weight measurement reference.
A Weighty Subject
Roman Emperor Constantine began reforming the empire's coinage around 309 BCE in order to counteract the debasement of coins that preceding rulers engaged in. Constantine began with creating a new highly pure gold coin, the solidus.
The solidus was divided into 24 siliqua. In this way, units of currency were also direct measurements of weight. Recall from earlier that the Latin classification for the carob tree is Ceratonia Siliqua, so in terms of mass (weight), siliqua represented 1/24th of a standard gold coin.
The Divergence of Weight and Purity
The design features on highly pure gold coins wear away easily, so in order to make them easier to handle (and more useful for commerce), harder metals such as copper or silver were added to the coin alloys. Once this practice of alloying gold with other metals for coinage began, it made sense to describe the gold content in terms of parts per 24, using the siliqua standard mentioned above. This is where the term karat arose as a measure of gold purity, revealing the origin of the 24 parts used for modern purity measurements.
The solidus, with its 24 siliqua, weighed approximately 4.5 grams. This same standard was used for the Islamic dinar gold coins that followed, showing that the carob seed has been used as a standard across the world and throughout history, as well.
Read more interesting articles about gold, silver, and coins in the Gainesville Coins Learning Center.