Natural diamonds start out as carbon trapped as inclusions in hunks of rock, called xenoliths, some 100 miles below the Earth's surface.
Xenoliths must "cook" at about 2,000 degrees Fahrenheit then ride a spurt of lava to the surface, where the carbon can cool into diamonds at the edges of a carrot-shaped tube.
This is why commercial diamond mines are usually conical pits: Workers excavate walls of minerals (often kimberlite) hunting for diamond-containing xenoliths.
But beautiful diamonds do not need to be intensively dug out of billion-year-old lava pipes. Since 1954, diamonds have been grown inside laboratories in a variety of colors and purities.
For growing gemstones, the most popular method is called chemical vapor deposition (CVD). It starts with a tiny diamond seed which — like all diamond jewelry — is made of a repeating lattice of carbon atoms.
The seeds are placed inside a microwave plasma oven. The oven zaps natural gas into a plasma of carbon, which sticks to each seed and slowly builds up a diamond, atom by atom.
A company called Pure Grown Diamonds told Business Insider that it can take anywhere from 10 to 12 weeks to bake up a batch of substantially-sized diamonds in its Singapore lab.
This is why jewelry-grade synthetic diamonds aren't cheap — and why actor Leonardo DiCaprio and 10 billionaires have invested in Diamond Foundry, which claims it can cut the time to a few weeks.
Diamond Foundry's process also uses CVD, though at less pressure and at a higher temperature in a reactor that can reach 8,000 degrees Fahrenheit.
After the synthetic diamonds are grown to spec, they're cut into rough shapes with a high-power laser.
Most of the time they come out square to maximize the amount of synthetic diamond.
Next, just like natural diamonds, skilled workers polish the synthetic gems for faceting, Pure Grown Diamonds told us.
Any of the company's gems above 1/4 of a carat (a measure of diamond weight) are laser-inscribed with a registry number and graded by their color, cut, clarity, and carat.
The diamonds are then sold to retail outlets as synthetic, sustainable, and conflict-free diamonds.
Outside the jewelry store, you can find cheaper synthetic diamonds everywhere. Like these diamond-encrusted drill bits for powering through glass.
This diamond — a polycrystalline variety made into a single wafer, made by a company called Element Six— isn't for engagement rings. But the "super material" may be useful in radar systems, communications devices, and perhaps radio telescopes.
Other varieties of diamond, like this disc, can be scratch-free optics that go into lenses, lasers, and infrared cameras.
Synthetic diamonds are even making their way into high-end speaker systems as the perfect tweeter material.