A team of Brazilian researchers discovered the first direct evidence that goethite—the mineral responsible for the brown color of soils—can withstand extreme pressures and temperatures all the way to the planet's interior inside a diamond just 3 millimeters (0.1 inch) long, within a microscopic impurity. Goethite forms in soil and on the ocean floor from iron-rich minerals in the presence of water. It incorporates some of these water molecules into its mineral structure. The study suggests that goethite may transport and release water into a region known as the lower mantle.