Only 132 people can 'afford' to buy that 1,111-carat Botswanan diamond

There's an old rule of thumb when it comes to buying engagement rings: The person who is proposing should spend one month's income on it.

You can thank the good people at De Beers for this Great Depression-era marketing ploy.

But in the past week, a 1,111-carat diamond was unearthed in Botswana, the second-biggest ever, and was valued at $50 million.

So if you apply that pseudo-equation to this new find, then someone would have to make about $50 million per month to "afford" it for an engagement ring.

And that leaves us with 132 people in the world, according to Deutsche Bank analysts. (Or, the richest 0.0000019% in the world.)

In other words, even the majority of ultra-high-net-worth (UHNW) individuals, who by definition have a net worth of at least $50 million and make up the richest 0.00168%, shouldn't put this monster on an engagement ring.

"To reach a wider potential market, therefore, the stone will have to be cut," the Deutsche Bank analysts suggest. "That is a complicated task because diamonds are priced exponentially. A 3-carat rock, for example, can cost 10 times more than 1-carat sparklers."

Notably, that's sort of what happened to the biggest diamond ever, "the 3,106-carat Cullinan," which was found near Pretoria in South Africa in 1905: It was cut up and turned into the Great Star of Africa and the Lesser Star of Africa, which are set in the crown jewels of Britain.