There are less than 200 women billionaires in the world. Gina Rinehart is one of them. In fact, in 2012 she topped the list as the wealthiest woman in the world. Today, her wealth has declined a bit, but she's still worth an estimated $12.5 billion according to Forbes. That's enough to make her the wealthiest person in Australia.

How she accumulated all that wealth
Rinehart was born in Australia in 1954 and was the only child of Lang Hancock who founded Australian mining company Hancock Prospecting. When Lang died in 1992, it was Rinehart who took control of his privately owned mining empire as she became chairwoman of Hancock Prospecting. It's the near total control of that vast mining empire that has poured so much wealth into Rinehart's coffers.

Hancock Prospecting's value is derived from the rights it holds to some of the largest land leases in the Pilbara region of Australia. This resource-rich region is known primarily for its iron ore production. In fact, a large portion of Hancock's profits come from its joint ownership of the Hope Downs mine with global mining giant Rio Tinto (RIO 0.41%) as well as mineral royalties it receives from iron ore sales from a Rio subsidiary. Hancock also is involved in ferruginous manganese, uranium, molybdenum, lead, zinc, gold, diamonds, and petroleum.

Following in Oprah's footsteps?
While Rinehart's mining company has provided her the bulk of her wealth, she has been diversifying into media in recent years as she became the largest shareholder in Fairfax Media and a significant investor in Ten Network Holdings. This diversification serves two purposes for Rinehart. First, it helps lessen the blow when commodity prices slide, which they've done over the past couple of years. That slide is one reason why Rinehart lost her title as the world's richest woman just one year after attaining that top spot. In fact, her overall wealth has been nearly cut in half over the past few years as commodity prices have fallen, decreasing the value of her mining empire.

That wealth diversification aside, the other reason why Rinehart has been investing in media is because she is leveraging those investments to ensure that her views have a voice. Those views, which are pro-mining and conservative in nature, aren't always being espoused by the press in Australia. So, by investing in media companies she can ensure there will be a voice for free enterprise.

However, the moves have some in Australia worried that she'll turn into Rupert Murdoch and use her influence to choose editors that will shape coverage. This would lead to a perceived bias in the media to exert influence on public opinion. However, the ability to form public opinion is a very valuable commodity. It is what Oprah used to create her own media empire that made her a very wealthy woman as she's worth an estimated $3 billion. That wealth aside, Oprah's control of her platform ensures that she has control over the formation of the public opinion of her viewers. She is free to use the "Oprah Effect," which is the significant influence she has to use her media platform and her power to, for example, turn an unprofitable small business into an overnight success just by promoting the company on her show.

Rinehart has the potential to use the media in a similarly powerful way. According to Forbes she's already the 27th most powerful woman in the world and not too far behind Oprah, who is 14th on Forbes' list. While Rinehart is known for avoiding the press, she has used it to wield her power to change perception to great effect. In 2012, for example, the mining industry in Australia was under pressure after the government proposed a set of new taxes on the industry. She helped lead the fight against these taxes and one of the most memorable moments was when she jumped on the back of a truck and started chanting "axe the tax" while wearing a glittering pearl necklace. That stand eventually led to the ouster of the country's prime minister and a watering down of the tax plan.

Gina Rinehart's wealth has ebbed and flowed with commodity prices. That's one reason why she has diversified into media. However, she also knows that the media's power is a key to her ability to not only keep the wealth she has, but to create more wealth by influencing public opinion to ensure that the free market always stays open.