One morning a couple of weeks ago, I found myself atop a dirt mound, surrounded on all sides by green hills and trees, watching a man in a pit.Wearing a blue hardhat and matching shirt, he was slowly, steadily, tediously swinging a shovel into the muddy walls around him, paying no mind to the gawking tourists above. All of his attention was fixed on unearthing some shiny yellow nuggets: imperial topaz.The gemstone, which can range in color from dingy champagne to deep tangerine, is found almost exclusively here in Minas Gerais (Portuguese for “general mines”), Brazil. My tour guide said it fetches some $2,000 per carat.For all I learned that day about the country’s landscape, economy and the harsh business of mining, I didn’t entirely grasp the natural science behind these sparkling commodities. What created the imperial topaz? Why is it so rare? Why is it sometimes yellow and sometimes red? When I got home, I turned to the Gems and Jewels app on my iPad to fill in the blanks.Read more at...Download the Universe, March 2012.