A small mining firm just saw its stock surge 91% after it discovered the world's 2nd-largest diamond

• Shares of Lucara Diamond Corp. surged 91% Thursday after it discovered a 2,492-carat diamond.
• The diamond, found at the Karowe mine in Botswana, is the world's second-largest ever.
• Lucara's market value rose by just over $40 million on Thursday following the announcement.

Shares of Lucara Diamond Corp. soared as much as 91% on Thursday after the Canadian mining firm announced it had discovered a massive 2,492-carat diamond.

The diamond, which weighs about a pound and is about the size of a baseball, was discovered at Lucara's Karowe mine in Botswana.

That makes it the world's second-largest diamond ever discovered.

The uncut diamond is just over 600 carats smaller than the Cullinan diamond, discovered in South Africa in 1905.

Shares of Lucara traded on the Toronto Stock Exchange at a high of $0.63 on Thursday, nearly double their closing price on Wednesday. The stock has since pared its gains in afternoon trading to 33%.

While the rough diamond has yet to be thoroughly assessed and appraised, it is expected to be worth tens of millions of dollars — and it could be worth muhc more if it is considered a gem-quality rock.

In 2015, Lucara discovered a 1,109-carat gem-quality diamond at the same mine. The stone sold for $53 million.

Lucara's market valuation soared by just over $40 million on Thursday to nearly $150 million, according to data from YCharts.

What is unique about Lucara's find is that the diamond was discovered via X-ray technology.

The diamond "was detected and recovered by the Company's Mega Diamond Recovery X-ray Transmission technology, installed in 2017 to identify and preserve large, high-value diamonds," Lucara said in a press release.

"This find not only showcases the remarkable potential of our Karowe Mine, but also upholds our strategic investment in cutting-edge XRT technology," Lucara CEO William Lamb said.

Diamond miners have faced various challenges in recent years, from declining prices due to the rise of lab-grown diamonds to the underlying challenge of locating and extracting fragile gems without breaking them.