Lesson 4 from the Moon: Explosive Eruptions

Fire fountains happened on the Moon, producing dark, dispersed deposits (red arrows). These are frequently located along cracks in the surface, as here on the floor of the crater Alphonsis. (NASA photo.)

A lunar pyroclastic deposit was sampled at the Apollo 17 landing site. The deposit (seen in the lower right portion of the NASA photograph above) had a distinctive orange color, caused by its high titanium concentration, and was composed of millions of tiny droplets (seen in the photograph below).

Here is a thin slice of some Apollo 17 orange soil as viewed through a microscope. The view is only about one millimeter across. Most of the droplets are composed of glass. The darker ones crystallized only partially and formed the opaque mineral called ilmenite. (Photograph courtesy of Graham Ryder, Lunar and Planetary Institute.)

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