Geodigest

Abstract

When the penguins ‘poop’ on Antarctica’s Elephant Island, chemical reactions in the soil produce a dull brown mineral called spheniscidite (Jonathan Amos, BBC News, 2 July 2022). This mineral is unique and reflects the special conditions that exist only in that locality. The name comes from Sphenisciformes—the group to which penguins belong. Spheniscidite is just one of roughly 6000 such minerals that have been officially recognized recently by the International Mineralogical Association (IMA). But there have been some changes. Robert Hazen from the Carnegie Institution for Science in Washington DC has spent the past 15 years reclassifying the minerals to add information about their genesis. ‘There’s been a classification system in place for almost two centuries that’s based on the chemistry and the crystal structure of minerals, and ours adds the dimensions of time and formation environment’, he told the BBC. With colleague Shaunna Morrison, Hazen has tried to give the thousands of different mineral species some extra context, making the point that you cannot truly appreciate the significance of a mineral unless you also understand how and when it formed. Their research shows nature has used 57 ‘recipes’ to create 10 500 of what they like to call ‘mineral kinds’—by crushing, zapping, boiling, baking and more. For instance, water, they say, has helped more than 80 percent of mineral species to form. Biology has had a direct or indirect role in the creation of about 50 percent of mineral species, with onethird formed exclusively through biological processes. ‘Life affects minerals in various ways,’ explained Hazen. ‘For example, photosynthesis produces oxygen. Oxygen is a very reactive gas, and it changes the surface of Earth by oxidizing minerals. So more than 2000 new minerals formed on Earth as a result of oxygen in the atmosphere. But of course, life also creates its own minerals, biominerals. These are shells, teeth, bones, and other structures in organisms that are purposefully deposited and sculpted in the most amazing nanotechnology kinds of ways. Scientists and engineers would love to be able to reproduce what life is able to do’. Between them the scientists have built a database of every known process of formation for every known mineral species, 5659 of them in the IMA catalogue. For each mineral, they considered the ‘recipe’ needed to form them: the particular physical, chemical or biological processes involved. They found that some 40 percent originated in more than one way. According to Hazen: ‘The previous system of mineralogy said calcite is calcite; that is calcium carbonate in the calcite crystal structure, that is a species. But we say no, no, no—there are 10, 15 maybe 20 different kinds of calcite (Fig. 1), because the calcite deposited by a shell is very different from the calcite that forms on the ocean floor through just chemical precipitation, or calcite formed deep within the Earth in a process of metamorphism—of high pressure and high temperature. ‘So, we see many different kinds of calcite, and that is key to our new approach to mineralogy’.