The Carbon Mineral Challenge will officially end in September 2019, but this first-of-its-kind worldwide collaboration to identify new carbon minerals has seen an impressive haul. Since its launch in 2015, researchers and mineral collectors have identified 30 new carbon-containing minerals. This is a stunning accomplishment, and yet the diversity of new minerals discovered suggests that many more remain to be found.
DCO Extreme Physics and Chemistry Community member Daniel Hummer (Southern Illinois University, USA) sums up the accomplishments of the Carbon Mineral Challenge in a new paper  in the Australian Journal of Mineralogy. The DCO-sponsored initiative brought together scientists, industry geologists, museum staff, and amateur mineral collectors in a targeted search to identify new carbon minerals. The variety of the finds highlights the incredible diversity of forms that carbon minerals can take, and also shows the utility of using our knowledge of existing minerals to direct the search for the unknown.
“There’s a lot out there that we don’t know,” said Hummer. “It helps us to look at the big picture and make predictions about what’s out there so we’ll know exactly what tools to use, and where to search, to make discoveries more efficiently than we have in the past.”
In 2016, Hummer wrote a paper  with DCO Executive Director Robert Hazen and other DCO members that viewed Earth’s minerals through the lens of ecology. By treating different minerals like biological species, they could apply ecological models to make predictions of Earth’s total mineral diversity. Just like biological species, minerals have a distribution pattern where there are a few common minerals found in multiple places, but the great majority of minerals are rare. The model predicted that Earth had at least 548 carbon minerals. At the time, only 403 were named, leaving 145 yet to be discovered. The researchers also came up with more than 400 possible formulas for these unknown minerals.
Hummer and his colleagues thought, “How can we test whether these minerals exist?”
The researchers conceived of the Carbon Mineral Challenge. They launched the initiative during a press conference at the 2015 AGU Fall Meeting in San Francisco, and promoted it extensively by advertising with mineral societies, geological journals, the Mindat database of minerals, rocks, and meteorites, and at the 2016 and 2017 Tucson Gem and Mineral Show, the largest gem show in the world.
Throughout the challenge, scientists and mineral collectors identified a wide range of minerals from around the world, including ewingite, a uranium mineral from a Czech mine that has the most complex crystal structure ever seen, wampenite, which is a hydrocarbon that crystallized on a fossilized pine tree in Germany, and paddlewheelite, named after it’s paddlewheel-like structure. Hummer has not yet done a statistical analysis of how the results compare to discoveries in previous years, but the new finds represent a significant part of the predicted missing minerals, about 20 percent.
Surprisingly, only two of those minerals exactly matched predicted formulas, abellaite and parisite-(La). “We think that there is value in these predictive tools that we’ve developed in mineral ecology, but there are also limitations to them just because the chemistry of carbon is so diverse,” said Hummer. “There are so many different things that carbon can do geochemically that it gives rise to tremendous variety.”
Mineral discovery has accelerated in recent years, in large part because advanced microscopy techniques allow scientists to see and analyze tiny specimens of new minerals that we wouldn’t be able to identify otherwise. One example is bridgmanite, which scientists think is the most common mineral on Earth and makes up most of the mantle. No one had actually seen the mineral, however, until microscopy techniques revealed it in a meteorite, where bridgmanite formed from the extreme heat and shock pressure created when a meteorite collided with another body in space .
So far, mineralogists have identified more than 5000 total minerals, but scientists estimate that there may be more than 4000 left to find . One possible reason that Earth has such diversity is that life drives new minerals to form. The activities of microbes especially have impacted mineral diversity, but larger organisms play a role, as well. One of Hummer’s favorite new finds from the Carbon Mineral Challenge is tinnunculite, a mineral that forms from the heated, crystalized droppings of falcons.
Based on what we’ve learned so far, other planets don’t appear to have the same level of mineral diversity, which may be related to a lack of life. “I think it will be very interesting to compare the mineralogy we find here on Earth with other planets to see, is it that same pattern where most species are rare? Or is it a different pattern?” said Hummer.
Once the Carbon Mineral Challenge ends this fall, Hummer hopes that there will be new challenges on an even grander scale in the future.
“There are lots of different communities that have various expertise and strengths when it comes to searching for new minerals,” said Hummer. “I think we need new challenges and initiatives that unite those communities and get them talking to each other.”
Main image: Ewingite, identified during the Carbon Mineral Challenge, has the most complex crystal structure of any known mineral. Credit: Travis Olds