It was enough money for the poor miner to buy his family a house in the Colombian capital. And Casas says his lucky find got him hooked on working for virtually nothing, scouring the countryside for more of the green, precious stones.

In Colombia, the world's largest producer of raw emeralds, the story told by Casas is no anomaly. Many of the country's poor work without a salary for several local emerald mining concerns, hoping to pocket a few stones along the way and make their own small fortunes.

It's no easy way to earn a living. But for these poor Colombians, there's hope that better days may be on the horizon.

Some investment experts see growing demand for the stones in places such as Asia and the Middle East, where for religious and astrological reasons emeralds often have more appeal than diamonds or other precious gems.

Colombia, which has the largest emerald deposits in the world, is particularly well-positioned to benefit from this increased demand. Several countries in Africa also have large emerald deposits.

"I would look at emeralds as a way of playing the huge demand for luxury goods from China and the Middle East," said Caspar Trenthard, investment director for UK smaller companies at Standard Life Investment.

Standard Life is a shareholder in Gemfields PLC (GEM.L), a small company trying to position itself as the leader in emerald mining. Gemfields wants to move the business beyond its local-miner image and onto a bigger stage.

"Color-stone mining around the world is done on a very small scale, almost mom and pop," said Ian Harebottle, chief executive of Gemfields, referring to a model that has hampered Colombia from better exploiting the abundance of its natural resource.

NOT EASY BEING GREEN

Harebottle said his company, which is publicly traded on the London Stock Exchange's Alternative Investment Market, is trying to change that model. But one problem Gemfields faces is the lack of a uniform "grading system" for emeralds like there is for diamonds.

Clarity, brightness and color are established characteristics of diamonds. But the standards for emeralds are still in flux and not universally agreed upon, something that can affect pricing and profitability.

Gemfields' goal is to do what privately owned De Beers did for diamonds by creating a stable market for emeralds and enhancing the gem's image as more than an exotic coloured stone.

"We are very fortunate because we can look at De Beers' history and say: let's do what they did well, better, and let's avoid what they did wrong," Harebottle told Reuters in a telephone interview from the company's Kagem emerald mine in Zambia.

Gemfields begins with an advantage over De Beers in that emeralds do not have the stigma of "blood diamonds", or such gems mined in a war zone and sold to finance insurgency.

The company says it carefully promotes a mission to mine and market emeralds in an ethical, legal and environmentally friendly way to attract customers who want to know that its miners are well treated and do not work illegally.

Gemfields produces 20 percent of all the emeralds in the world, most of that coming from its mine in Zambia. It is the largest player in emerald mining and each month extracts 2 million to 3 million carats of the gemstones.

Carat prices for small, high-quality emeralds have risen 1,000 percent in the past three years to around $40 for a stone that is uncut and in the rough, according to industry analysts.

In the past three years, Gemfields' stock price has soared from 3 pence a share to 38 pence a share on the AIM.

But its small market capitalization of $208.5 million has kept some investors away. Other money managers are worried that a single shareholder, a division of South African-based private equity firm Pallinghurst Group (PGLJ.J), owns 63 percent of Gemfields.

RISK FACTORS

Political risk is also a factor, as a change in Zambian government policy could negatively affect the company's operations. It's one reason Gemfields is looking at Colombia as a place to open a second mine, said a person familiar with the company but unauthorized to speak for it.

Ironically, after years of drug violence and political corruption, Colombia is now seen as a more hospitable environment for some mining operations.

In addition, the company's long-term prospects come down to supply and demand. Like any other gemstone producer, Gemfields' business remains sensitive to consumer preferences and disposable income.

"We are selling a luxury good. It is not food, it is not fuel, so there is a dependence on people's ability to buy something of luxury," Harebottle said.

Yet some analysts view this alternative market as a solid diversification tool, and a good store of value, in an adventurous investor's portfolio given its upward trajectory in an otherwise sputtering global economy.

"As liquidity in the company improves, Gemfields is starting to get a broader audience of investors who are having a look at it because they can actually make some good money," said Alexander Mees, equity analyst at JP Morgan Cazenove.

That said, it is unlikely that diamonds will be overtaken as the top-selling precious stone anytime soon. But in a world where high-yield investments are few and far between, some believe coloured gemstones such as emeralds are making a mark.

"People are looking for a safe haven to put their dollars, which are worth less every day, into something that has strong intrinsic value or something that will appreciate," said Jeffrey Roseman, president of David Harvey Jewelers Inc, based in Darien, Connecticut.

"There is no question people are seeking fine gemstones."

(Editing by Jennifer Ablan, Matthew Goldstein and Dale Hudson)

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