Knowledge
18.04.2020 ABOUT THE SIZE & WEIGHT OF GEMSTONES
The weight of a gemstone is measured in carats (ct). One carat equals 0.2 grams, or, in other words, 1 g = 5 ct.
This means that certified gemstone weights are generally accurate to one-hundredth of a gram, or, in rare cases, one-thousandth of a gram.
Karat or Carat?
When discussing gemstones, carats are not the same as karats when discussing gold. For gold, karats (kt) describe the purity of the alloy. Pure gold is 24 karats; 18 karat gold is 750 gold (75% pure gold); and 14 karat gold contains only 58.5% pure gold (585 gold).
The carat unit allegedly originated with the dried seeds of the carob tree, which were used as balance weights for measurement. In reality, the carat differed from country to country until 1907, when the metric carat was introduced as an international standard. Since then, a one-carat stone has weighed 0.2 grams.
It wasn’t until 1907 that the metric carat (carat métrique), with its value of 0.2 grams, was introduced as an international unit of measurement.
How big is a one-carat stone?
Generally, the “size” of a gemstone refers to its weight. The actual dimensions of a one-carat stone depend on the density of the mineral and the type of cut.
For example, a one-carat brilliant-cut diamond has a diameter of 6.5 mm, while a one-carat round-cut ruby is only 5.35 mm in diameter. This is due to the difference in the specific density of the two gemstones.
the world’s largest gemstones
The largest rough diamond ever found—internally flawless, no less—was discovered in South Africa in 1905 and named “Cullinan” after the mine’s owner, Thomas Cullinan. The 3,106.75-carat diamond was divided into many pieces. The nine largest stones (Cullinan I–Cullinan IX) are part of the British Crown Jewels.
The world’s largest cut ruby is the Liberty Bell Ruby. Weighing 8,500 carats (1.7 kg), it was cut in the form of the Liberty Bell to celebrate the United States Bicentennial. However, this stone is opaque.
The largest sapphire was found in Sri Lanka as recently as 2015. The “Star of Adam” weighs 1,404.49 carats (just under 281 grams).
Considered “a gift from God,” the largest cut emerald in the world is named “Teodora” and weighs 57,500 carats — that is 11.5 kilograms. However, experts doubt its authenticity.
Price per carat: how much does one carat cost?
Unlike precious metals, it is not possible to define a standard price per carat for gemstones.
In contrast to precious metals, it is not possible to define a standard price per carat for gemstones. The following characteristics strongly influence the value of a gemstone:
- Naturally colored or treated
- Color and intensity (saturation)
- Clarity
- Source
- Cut type
- Certificate
Dr. Thomas Schröck
The founder and managing partner of THE NATURAL GEM has been active in international gemstone trading for 30 years. As a doctor of economics and a certified gemmologist in Switzerland, Germany and the USA, among other countries, he is one of Europe’s leading experts on naturally-coloured, untreated gemstones and investments in them.
