Conventional wisdom would suggest that cultivating a diamond above the ground takes a lot more energy than extracting an underground diamond that Earth has already created.  After all, diamond is created using intense amounts of temperature or pressure — so once formed, it should not take so much energy to harvest it.

We researched the facts. It turns out it takes an entire factor more energy to extract an underground diamond from Earth than it takes to cultivate one above the ground in a foundry.  

Then, of course, the energy used in mining is generally dirty Diesel versus renewable energy in our above-the-ground production.

The amount of energy required for underground mining is quite surprising — and a testament of how far innovation in above-ground diamond cultivation technology has progressed over the years as well as how inefficient mining of underground diamonds tends to be, having to move huge quantities of soil in often highly remote areas.

The Facts: kWh per Carat Consumption

Diamond mines operated by De Beers consume an average of 80.3 kWh per carat. The Canadian Diavik mines consumer 66 kWh per carat. [1, 2, 3]

Each of these is an entire factor higher than what creating a diamond in a laboratory takes using the best available modern technology.

The number touted often by the mining industry is the Australian Argyle mines at 7.5 kWh per carat. That’s significantly lower than the other mines — but the material produced in these mines tends to be lower quality rough as well.

Note that a carat is just a weight metric: one fifth of a gram. It says nothing about the quality or the value. A flawless 5-carat sized diamond is completely different than a splinter of a brown diamond. The difference in value can be orders of magnitude. For example, according to [4], 80% of the diamonds produced in the Argyle mine are brown and have little value:

Before the development of the Argyle diamond mine in Australia in 1986, most brown diamonds were considered worthless for jewelry; they were even not assessed on the diamond color scale, and were predominantly used for industrial purposes. However, marketing strategies changed in the 1980s and brown diamonds have become popular gems. The change was mostly due to supply: the Argyle mine, with its 35 million carats (7,000 kg) of diamonds per year, makes about one third of global production of natural diamonds; 80% of Argyle diamonds are brown. 

The Facts: Energy per Gem Quality Carat

A true apples-to-apples comparison needs to look at the value produced versus the energy consumption. Those numbers are actually not hard to get hold of — it’s effectively just the wholesale value per total carats produced.

De Beers recently produces diamonds at a wholesale value of $187 per (rough) carat. Alrosa produces diamonds in a way that 58% of the mining output is at a value of $166 per (rough) carat and 42% of the output has a value $10 per (rough) carat. [6] That’s an average of $100 per (rough) carat.

Manmade diamonds have much higher quality and yield. Effectively the entire yield of a diamond foundry is 5-carat and larger (rough) diamond. No brown material. All high-value, pristine quality. The market prices of this in the global wholesale markets is an entire factor higher.

The net of all of this is that, on an apples-to-apples comparison, foundry diamonds require an order of magnitude less energy to make than mined diamonds require to harvest.

Cudos to the elegance of technological development!

High Carbon Diesel versus Renewable Electricity

Then the type of the energy used is very different of course: Mining in remote areas tends to require the use of Diesel generators whereas diamond foundries can be located in areas where they use solar power and other renewable sources of electricity.

This means that regardless their energy consumption, foundry diamonds can be sustainably created whereas mined diamonds have a very large carbon footprint.

Still what is perhaps more surprising is the sheer amount of energy involved is so high for mining. This in turn speaks to the fact that mining is very hard work — it requires moving hundreds of tons of soil for the hope of finding some good carats, etc.  But is is anything but sustainable.

The Facts: Total Environmental Footprint

An independent audit conducted on the total environmental footprint of various diamond mines and foundry producers show how vastly more environmental above-the-ground "mining" (in a foundry) is relative to underground mining:

At Diamond Foundry, our footprint is so small, we were capable of making it 100% carbon neutral -- and get to the point where Diamond Foundry is now certified 100% carbon neutral.

Sources & Further Reading:

(1) https://www.uvm.edu/~shali/Synthetic_Diamonds_Mined_Diamonds.pdf

(2) https://alumni-gsb.stanford.edu/get/page/magazine/article/?article_id=30353

(3) http://www.slate.com/articles/health_and_science/the_green_lantern/2010/08/something_old_something_new_something_borrowed_something_green.html

(4) https://en.wikipedia.org/wiki/Brown_diamonds

(5) http://www.idexonline.com/FullArticle?Id=42878

(6) http://eng.alrosa.ru/alrosa-reports-q4-and-fy-2015-production-and-preliminary-trading-performance/