An interesting avenue of research for me is when someone reviews older results that were either wrong or just not sufficiently right. This story starts in the 1840s when two German mineralogists, Rudolf Hermann and August Breithaupt published separate papers positing the existence of an iron-poor version on hematite that contained water. The name that has stuck for this proposed mineral was hydrohematite, which makes perfect sense. However, in the 1920s, scientists using this new fangled X-ray diffraction technique said those papers were wrong. 

Enter graduate student Si Athena Chen, who set out to crystalize hematite and ended up with an iron-poor version. This led her to seek out old samples that supposedly contained water and test them, including Breithaupt’s original sample. Technology has come a long way since the 1920s, and X-ray diffraction has drastically improved. Plus, Chen had at her disposal other advanced instruments. And what she found was that the samples were indeed iron-poor and had hydroxyl, OH, substituting some of the missing iron. Voila! Hydrohematite. 

Who cares? Scientists studying Mars have found bright red pebbles on Mars that are now called “blueberries” and are thought to be hematite. Chen’s experiments found that hydrohematite formed at temps lower than 150 degrees Celsius, from watery, alkaline environments, similar to what we think Mars had available in its watery past. The mineral forms in spherical structures here on Earth, so it’s possible that the blueberries are the same. Now we just need more data from Mars. The rovers have X-ray diffraction instruments, but they aren’t sensitive enough to tell the difference between hematite and hydrohematite, so definitive answers may have to wait until the Mars Sample Return mission happens.

More Information

Penn State press release