This question has caused a lot of debate within the diamond industry, as well as among its consumers who are just starting to educate themselves on lab-grown diamonds and how they are made. In reality, their physical appearance is essentially identical to those mined from the Earth, with any differences being invisible to the naked eye. Both forms also share extremely similar chemical properties, considering both are made from pure carbon. When it comes down to it, distinguishing what makes them different only comes down to the subtlest differences.
The main difference is the shape in which these diamonds grow. Natural diamonds, as shown in the diagram, typically grow into an octahedron shape. Lab-grown diamonds, however, vary in shape depending on which method is used to grow them. Using High Pressure, High Temperature (HPHT) — which mimics the natural conditions that mined diamond experience within the Earth — can cause the gem to grow into what is called a “cuboctahedron”, which includes 14 different directions of growth! Chemical Vapor Deposition (CVD), which involves breaking down molecules of carbon gases into carbon and hydrogen atoms and depositing it onto a diamond seed to grow, tends to grow into a cubical shape. Because these are the diamonds in their “rough” state, most consumers will never see these natural growth shapes and will only see them as perfectly cut gems ready to be bought.
The Gemological Institute of America (GIA) offers “diploma programs” or official GIA credentials on lab-grown diamonds. GIA grading reports for LGDs look very different to reports for mined diamond, with different terms being used to describe the 4Cs (color, cut, clarity, and carat), and broader categories are applied when it comes to sorting gems. The institute also hosts seminars that teach the process of diamond grading, as well as the latest methods used to tell the difference between earth-grown and lab-grown. To see the physical differences for yourself, you would need sophisticated laboratory equipment to view and compare them up-close.
There are many methods consumers can use to ensure they are purchasing the diamond they want, whether it be mined or lab-grown. The GIA has been focused on disclosing reports with consumers about lab-grown diamonds for over 10 years and will continue to do so as the laboratory-grown diamond industry grows.