THE SHORT ANSWER
It is carbon, arranged the same way.
A mined diamond formed under pressure in the earth. A lab-grown diamond formed under pressure in a reactor. The resulting crystal is the same material with the same hardness, the same refractive index and the same fire.
The distinction is origin, not substance. That is why the trade calls them lab-grown rather than synthetic or simulated. A cubic zirconia is a simulant, a different material pretending to be a diamond. A lab-grown diamond is not pretending to be anything.
Two methods dominate. High pressure high temperature recreates the conditions of natural formation. Chemical vapour deposition grows the crystal layer by layer from a carbon-rich gas onto a diamond seed. Both produce genuine diamond.
Not with a loupe, and not by eye. Identification requires laboratory instruments that read growth structure and trace elements. This is exactly why certification matters: the certificate, not the appearance, is what tells you what you own.
The International Gemological Institute grades the stone independently on carat, cut, colour and clarity, and records its origin. The report is issued by the laboratory, not by the seller, which is the entire point of it.
They avoid the supply-chain questions that surround mining, which many of our clients care about. They are not free of impact: growing diamond is energy intensive, and the honest position is that the footprint depends on how that energy was generated.
This is the trade-off. Lab-grown production has scaled fast and prices have fallen with it, so the secondary market is weak and unpredictable. If you are buying something to wear and pass on, this does not matter. If you are buying a store of value, a mined stone is the better instrument, and we will say so, because we trade those as well.
Because a certificate tells you the grade and nothing about how the stone looks on a hand in daylight. Two stones with identical paperwork can perform very differently. Seeing them side by side is the part that cannot be done through a screen.
Same
HARDNESS, 10 ON THE MOHS SCALE
Same
REFRACTIVE INDEX, 2.42
IGI
INDEPENDENTLY GRADED
24 yrs
IN THE DIAMOND TRADE