Summary

Low calcium content pyroxenes are called orthopyroxenes and the most common encountered on the lunar surface are rocks containing some amount of norite.  The greater the amount of iron present, the greater the band depth and the more mafic the terrain is.  Amounts of iron under about 5% are not very mafic and are typically anorthositic.  Such terrain constitutes the majority of the lunar highlands.   The peaks are largely noritic, but with some mixed composition present in some areas.  Noritic features usually have band centers under 0.95 microns and band depths significantly greater than 5%.  FWHM band width is usually significantly less than 0.3 microns.

In contrast, high calcium content pyroxenes are called clinopyroxenes.  Small amounts of clinopyroxenes, typically less than 5%, are found in the rather anorthositic soils of the lunar highlands.  More mafic clinopyrene content is found in mare basalts and in the central peaks and walls of some craters such as Tycho.  Clinopyroxenes gave band centers between 0.95 microns and 1.0 microns.  Their FWHM widths are similar to those of orthopyroxenes. Olivine has a band center above 1.0 microns and the most well known olivine rich area is the central peak region of the crater Copernicus.  Some lunar mare also contain significant amounts of olivine.  Pure olivine is called dunite and lesser amounts are referred to as troctolite.  The FWHM width of olivine is wider than that of orthopyroxene or clinopyroxene and is usually greater than 0.3 microns.

Lunar features that lack iron content and so show no absorption trough near 1.0 micron and lack other minerals such as ilmenite, are likely to be more purely anorthositic.   

 

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