The quality and value of diamonds are determined by the "4C":
CUT / COLOUR / CLARITY / CARAT
The better the quality, the more expensive the diamond.
It should not be confused with shape.
A well-cut diamond, regardless of its shape, reflects incoming light better, is more brilliant, and has more fire. A brilliant-cut diamond is a polished diamond with at least 56 facets plus the table and culet (tip of the stone). The most common shapes are illustrated below.
The best quality of a diamond is its complete colorlessness. In an absolutely colorless diamond, white light effortlessly penetrates the stone and emerges in the colors of the rainbow.
In addition to the yellow series, diamonds also come in other natural colors.
Besides the natural colors, there are artificial colors (canary, cognac, petrol), which are achieved through irradiation.
Most diamonds have very small natural features called inclusions. The fewer and smaller these inclusions are, the better light can penetrate the stone.
For the experienced professional at 10x magnification.
The weight of a diamond is measured in carats. One carat consists of 100 points. So, the weight of a 75-point diamond corresponds to 3/4 or 0.75 carats.
One carat weighs 0.2 grams.