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Shown above is a montage image of Kilbourne Hole, an oustanding example of a volcanic maar, located in southern New Mexico. The view is looking east. At this point the crater is approximately one mile wide. The large white area in the bottom of the crater is a dry lake. The black arrows note portions of the Afton basalt that form the flat portions of the rim. Blocks of dark basalt have sloughed off the edges and cascaded down to the bottom of the crater. The basalt explosion breccia, composed of basalt fragments, olivine xenoliths, ash, and other rock fragments, is noted by green arrows. This breccia forms the grayish ridges that top the Afton basalt. It is the breccia from which olivine nodules weather. Rarely, the olivine nodules contain gemmy fragments of peridot that are large enough to be cut into gemstones.
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