Diamonds are the heaviest and densest material known to man. Diamonds are weighed in carats. A carat is .2 grams. A gram of diamond would be a massive 5 carats. Very large in diamond terms although the actual diamond is small.
A carat is further divided into Points, and there are 100 Points to a carat. So 1 point is .002 of a gram. Very small indeed.
There is a scale of weight for Diamonds and this is shown here:
| Weight | Size (diameter) | Weight: pts (diameter) | Weight: fractions |
| 0.10ct | 3.00mm | 10pts | 1/10th |
| 0.20ct | 3.85mm | 20pts | 1/5th |
| 0.05ct | 1.00mm | 5pts | 1/20th |
| 0.25ct | 4.10mm | 25pts | 1/4th |
| 0.33ct | 4.55mm | 33pts | 1/3th |
| 0.40ct | 4.80mm | 40pts | 4/10ths |
| 0.50ct | 45.15mm | 50pts | 1/2th |
| 0.66ct | 5.72mm | 66pts | 2/3th |
| 0.75ct | 6.00mm | 75pts | 23/4th |
| 0.90ct | 6.40mm | 90pts | 9/10ths |
| 1.00ct | 6.65mm | 100pts | 1 carat |
| 1.50ct | 7.50mm | 150pts | 1&1/2 carats |
| 2.00ct | 8.10mm | 200pts | 2 carats |
Due to the minute differences in the weight of most diamonds they should always be accurately weighed on an electronic scale to the nearest 1000th of a carat (.001). Stones are always rounded up or down to the nearest 1000th of a carat by the way.
The other factor to consider with weight is a certificate. Where a diamond has been assessed and weighed at a laboratory, a certificate should be issued to confirm the assessment. No stones should ever be purchased without a certificate from a bona fide laboratory.
| Code | Laboratory |
| ADL | Antwerp Diamond Laboratory |
| AGA | American Gem Apraisal Laboratories |
| CIB | CIBJO (Europe) |
| CSA | Jewellery Council of South Africa |
| DGL | Diamond Grading Laboratories (London) |
| EGI | European Gemmological Institute (Antwerp) |
| EGL | European Gemmological Institute (Antwerp & London) |
| PNF | P N Ferstenberg Pbv A |
| GAG | Gesellschaft fur Angewandte Gemmologie |
| GAN | Gemological Institute of Antwerp |
| GIA | Gemological Institute of America |
| GII | National Gemological Institue of Israel |
| GIL | Gem Information Laboratory |
| GTL | Gem Testing Laboratory of Great Britain |
| NGL | Northern Gemmological Laboratories (UK) |
| HRD | Diamond High Council (Antwerp) |
| HRG | Heinz R Gartner, DGemG, FGA (Germany) |
| IGI | International Gemmological Institute (Antwerp) |
| PSL | Precious Stone Laboratory (London) |
| VPT | Verena Pagel-Theisen, DGemG FGA (Germany) |
| WG | Werner Galia, DGem, (Germany) |
A complete list of laboratories with address and contact numbers is available at Lab List
It cannot be iterated enough to ensure that all diamonds you buy should have a certificate from one of the above laboratories.
See also Diamond Appraisal
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