The Natural History Museum of Los Angeles County last week unveiled the "Blue Moon Diamond," a 12 carat gem regarded as one of the rarest stones in the world because of its remarkable color, size and clarity.

The Blue Moon Diamond will be on display until January 6, 2015.

The Blue Moon Diamond is internally flawless.  It weighs 2.4 grams and is 0.61 inch at its greatest diameter. It was cut from a 29.6 carat rough diamond into a cushion-cut shape.

Like Us on Facebook

Its natural, uncut form was bought for US$25.6 million by diamond firm Cora International earlier this year. The diamond was discovered at the famous Cullinan mine in South Africa.

A 3,106 carat diamond discovered in the Cullinan mine in 1905 is still the biggest natural, rough diamond ever found. After being presented to King Edward VII, the two principal gems from this diamond later formed the British crown jewels. 

According to Eloise Gaillou, a mineral expert from the Natural History Museum, the Blue Moon Diamond is the first of its kind discovered in over 100 years.

Diamonds are formed in the mantle of the Earth, which is roughly 90 miles below the surface, as liquid carbon cools down and hardens into diamond form.

What makes the Blue Moon diamond unique and rare is its color caused by impurities mixed with carbon and boron, which is trapped inside the chemical structure of the diamond. Only one in 200,000 diamonds possess a blue hue.

Gaillou adds that the boron that causes the distinct blue color of the diamond was trapped during the formation of the Earth.

The museum's collection includes about 3,000 gems and stones from at least 150,000 rock specimens, minerals and meteorites. Almost all these precious stones are indigenous to California.

TagsRare Blue Moon Diamond Featured in L.A. Museum; What Makes It Blue?, blue moon diamond, diamonds, blue diamonds, natural history museum, LA, US, what makes blue diamonds blue