Home Jewels Gemstones Bespoke Royal Menagerie Haru Collection Contact
© Hampson Fine Jewels 2012
Most if not all gemstones are measured in carats (ct). The carat is a unit of weight, and not an indication of quality*.
The carat has been used for hundreds of years as the measuring unit for precious stones. It derives from an Arabic word for a small, regularly sized seed that was used as a weight.
Since 1914 the metric carat has been internationally standardised as 0.2 grams, so a stone weighing exactly 5 carats weighs 1 gram. The carat is further broken down into 100 ‘points’ - 50 points = half a carat, 25 points = a quarter carat.
To put the carat into perspective, the average diamond solitaire engagement ring in the UK weighs 25 points (a quarter carat). The largest cut diamond in the world weighs 545.69 ct. The largest polished gemstone in the world weighs over 35,000 ct. The whole of planet earth weighs somewhere in the region of 3027 ct… give or take a few!
Pearls are usually no longer sold by weight and instead are graded  by their diameter measurement in millimetres.
*Gold quality, or rather gold purity is referred to in carats, or sometimes ‘karats’ (kt).
Pure gold (1000/1000) is called 24 carat. Eighteen carat gold is 75% pure gold (750/1000) and 9 carat gold is 37.5% pure (375/1000).
Gold is alloyed with other metals like copper, silver or palladium to improve its durability or alter its colour. Pure gold (24 carat) is too soft for practical wear. The gold content is stamped into the article as part of the hallmark.
The other precious metals, platinum, silver and palladium are not measured in carats.
This ‘carat scale’ shows how the diameter of a standard brilliant cut diamond increase with the stone’s weight. As the stone gets heavier, the perceived increases are less pronounced.
As all gemstones are sold by weight (carats), it is understandable then that the carat weight has a direct influence on the cost of a stone.
If all other aspects are equal, the larger of two stones will always cost more.

Amongst other considerations that will effect the price are:

The quality or desirability
of the colour

The lack of inclusions effecting clarity

The quality of the cut and/or attractiveness
of the shape

Lack of artificial treatments - heating, irradiation etc.

Sometimes a geographic
or historic provenance