Earthly rocks point way to water hidden on Mars A combination of a once-debunked 19th-century identification of a water-carrying iron mineral and the fact that these rocks are extremely common on Earth, suggests the existence of a substantial water reservoir on Mars, according to a team of geoscientists. “One of my student’s experiments was to crystalize hematite,” said Peter J. Heaney, professor of geosciences, Penn State. “She came up with an iron-poor compound, so I went to Google Scholar and found two papers from the 1840s where German mineralogists, using wet chemistry, proposed iron-poor versions of hematite that contained water.”