Strange crystal birth found in mine

Shortly after its close in the 1960s, a mine in Tennyson, Wis., flooded with groundwater. Recently, scuba divers exploring the mine’s spooky depths spotted unusual, spongy red masses. The red slime, it turns out, contains the first evidence of a type of crystal formation seen previously only in laboratories.

Generally, crystals form when atoms or molecules in a solution slowly stack together. Over the past decade, however, researchers including Jillian F. Banfield at the University of Wisconsin–Madison have grown crystals from larger starting particles called nanocrystals, each with hundreds or thousands of atoms or molecules.

It turns out that the laboratory was imitating life. After viewing the scuba divers’ videotapes and using electron microscopy on samples from the mine, Banfield and her colleagues found that iron-oxidizing bacteria produce 2-to-3-nanometer-wide iron oxyhydroxide units that then aggregate.

“They don’t just stick together in a random orientation,” says Banfield. “They’ll rotate into structural accord with the adjacent particles.”

The nanocyrstal process could be useful to materials developers, Banfield says. When these large particles stick together, they trap impurities at the interfaces. Crystals formed in this way could incorporate unusual distributions of elements and compounds, she says. Silicon semiconductors rely on this kind of elemental spicing.

Since Banfield and her coworkers reported their results in the Aug. 4 Science, they’ve found sulfate-reducing bacteria in the same mine. These microorganisms produce zinc sulfide nanocrystals that aggregate in a similar fashion, she says.

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