Diamonds are formed from carbon, including those manufactured by man.
The diamond-looking synthetic stone Cubic zirconia --CZ -- is the crystaline form of zirconium dioxide (ZrO2). Other diamond-looking synthetics are formed from other minerals.
Man-made diamonds are often referred to as synthetic diamonds or lab-created diamonds.
Synthetic diamonds can be made in a sustainable manner. Mined diamonds are not sustainable.
There are several companies that create synthetic diamonds or cultured diamonds. One such company that creates the best synthetic diamonds is New World Diamonds.
Synthetic diamonds have the same hardness as real diamonds because they are made of the same material, carbon atoms arranged in a crystal structure. Both synthetic and real diamonds are the hardest natural material known, scoring a 10 on the Mohs scale of mineral hardness.
The difference is big: synthetic diamonds are real diamonds and repeat all properties of natural diamonds, simulants are just trying to copy the brightness of the valuable gemstone. Synthetic's price is usually much higher than simulants. For more information on simulants and real diamonds follow the attached link.
You can read more about synthetic diamonds, below, which first became possible -- as a recurring phenomenon -- in the 1950s.
Synthetic diamonds and real diamonds both have the same level of hardness. They both rank 10 on the Mohs scale of hardness.
Diamonds are made artificially by simulating the conditions deep in the mantle where natural diamonds are formed: very high pressure and very high temperature. Any source of carbon can be used (I saw a documentary on making diamonds once where they used peanut butter to provide the carbon). Synthetic diamonds will always be less expensive than natural diamonds, therefore the jewelry business now requires natural diamonds that have been cut to have LASER etched identification codes to prove authenticity. This only became necessary after techniques were perfected to reliably get colorless synthetic diamonds.
Natural diamonds are formed deep within the Earth over millions of years, while synthetic diamonds are created in a laboratory setting using high pressure and temperature. Natural diamonds are rare and can vary in quality, while synthetic diamonds are more consistent in quality and can be produced in larger quantities. Additionally, natural diamonds may have imperfections and inclusions, while synthetic diamonds are typically more flawless.
Gemesis is a company that grows yellow diamonds. These are known as synthetic, lab created, lab grown or cultured diamonds. Synthetic diamonds are real diamonds and also produced by D.NEA, Apollo and Chatham.
Natural black diamonds are rare. They are due to dark graphite inclusions. Their rarity makes them valuable. Most black diamonds are synthetic and made by heat treating low quality diamonds. The price of a synthetic black diamond is lower than that of white diamonds.
Diamond Nexus offers both synthetic diamonds(made with pure carbon) as well as diamond simulants that are not made with pure carbon, but are nearly identical to a natural diamond besides having different elements. The pure carbon gems are only available in a canary color though.