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Forget Green Cheese: Moon Silica Rich

Scientists have discovered massive silica-rich deposits. But before you rush to obtain mineral rights and mining permits, bear in mind, the deposits are on the Moon

Scientists have discovered massive silica-rich deposits. But, before you rush to obtain mineral rights and mining permits, bear in mind, the deposits are on the Moon.

Using data from the Diviner Lunar Radiometer, an instrument capable of identifying common lunar silicate minerals, scientists at Stony Brook University in New York and NASAís Jet Propulsion Laboratory found previously unseen compositional differences in the crustal highlands of the Moon, and have confirmed the presence of anomalously silica-rich material in five distinct regions.

ìIn laymanís terms, we have discovered a new and fundamentally different type of rock on the Moon,î says Timothy Glotch, assistant professor in the department of geosciences at Stony Brook and lead author of one of two papers on the research in this weekís issue of Science. ìFor decades, weíve recognized that these spots in the crustal highlands of the Moon are different. Now we have the evidence. The Moon is more geologically complex than previously thought, and we now have to refine our ideas about its formation.î

Every mineral--and, therefore, every rock--absorbs and emits energy with a unique spectral signature that can be measured to reveal its identity. For the first time, the Diviner Lunar Radiometer is providing scientists with global, high-resolution infrared maps of the Moon, enabling a definitive identification of silicates commonly found within its crust.

ìDiviner is literally viewing the Moon in a whole new light,î says Benjamin Greenhagen of NASAís Jet Propulsion Laboratory, lead author of the other paper. ?

Lunar geology can be roughly broken down into two categories: the anorthositic highlands, rich in calcium and aluminum, and the basaltic maria, which are abundant in iron and magnesium. Both of these crustal rocks are deemed by geologists as primitive; that is, they are the direct result of crystallization from lunar mantle material. Divinerís observations have confirmed that most lunar terrains have spectral signatures consistent with compositions that fall into these two broad categories. However, they have also revealed that the lunar highlands may be less homogenous than previously thought. In a wide range of terrains, Diviner revealed the presence of lunar soils with compositions more sodium-rich than that of the typical anorthosite crust. The widespread nature of these soils reveals that there may have been variations in the chemistry and cooling rate of the magma ocean, which formed the early lunar crust, or they could be the result of secondary processing of the early lunar crust.

Most impressively, in several locations around the Moon, Diviner has detected the presence of highly silicic minerals such as quartz, potassium-rich, and sodium-rich feldspar--minerals that are only ever found in association with highly evolved lithologies (rocks that have undergone extensive magmatic processing). The detection of silicic minerals at these locations is a significant finding for scientists, as they occur in areas previously exhibiting anomalously high quantities of the element thorium, another proxy for highly evolved lithologies.

ìThe silicic features weíve found on the Moon are fundamentally different from the more typical basaltic mare and anorthositic highlands,î says Glotch. ìThe fact that we see this composition in multiple geologic settings suggests that there may have been multiple processes producing these rocks.î

Some of the silicic features, such as the Gruithiusen Domes, possess steep slopes and rough surfaces suggesting that they may be lava domes created by the slow extrusion of viscous lava on the lunar surface (similar to the dome which formed on Mt. St. Helens after its eruption). In other regions, such as Aristarchus, the silicic spectral signatures are confined to impact craters and their ejecta blankets. This suggests that excavation of the subsurface caused by these impacts has exposed portions of plutons, which are magmas bodies that solidified underground before reaching the surface.