Why is breccia so common on the moon

In terrestrial sedimentary rocks, clasts often are aligned in the same direction because the Earth has more gravity than the Moon. In lunar breccias, the clasts are usually not rounded. In terrestrial sedimentary rocks, clasts are often rounded because the pebbles from which they form were rounded by abrasion against each other in water or ice before they were cemented into a new rock. Note also that aspect ratio length to width is short, almost always less than 3.

Elongated clasts and phenocrysts are more typical of terrestrial rocks. In most, but not all, lunar regolith and fragmental breccias, the matrix is darker than the clasts. A petrographic thin section of Apollo 17 sample , another fragmental breccia fov: 38 mm. At the far left is a breccia in a breccia in a breccia.

The dark clasts are glassy breccias, the white clasts are anorthosites. In both of these rocks, the vesicles occur only in the fusion crust, not in the interior of the breccia.

This portion of Apollo 15 sample consists of three pieces totaling g. The sample was collected near Hadley Rille where the soil consists mainly of mare basalt. The sample is a regolith breccia consisting mostly of nonmare material, however, but with some mare basalt. The largest piece of sample is about 5 cm in longest dimension. The large clast at the top is a mare basalt. Medium-sized piece of sample , 13 cm, with a large mare basalt clast at the right.

The green stuff at the edges is epoxy. The dark clasts are KREEPy impact-melt breccias and the light clasts are anorthosites, usually brecciated. These lava flows are about 35 meters feet thick near their margins. The direction of flow was from the lower left toward the upper right corner of this photo. The dark, flat often circular regions called lunar maria singular form: mare are composed of the rock basalt.

This basalt sample was collected near the rim of Hadley Rille. The fine-grained crystallinity and large holes indicate that this rock crystallized near the top of a molten lava flow. The grey color of this rock is due to the presence of dark-colored minerals. Regions of both the near side and far side of the Moon not covered by mare basalt are called highlands. The highlands consist of the ancient lunar surface rock, anorthosite, and materials thrown out during the creation of the impact basins.

Relatively young basins are shown in light colors; the oldest basins are in dark colors. The ancient crust of the Moon is believed to have been composed of the rock, anorthosite, a calcium-rich white rock. This ancient crust has been smashed and redistributed by countless meteoric impacts. One explanation for the presence of anorthosite in the lunar crust is based on the assumption that the Moon was once molten. Plagioclase, a relatively light mineral, crystallized as the Moon cooled and solidified.

This mineral floated toward the surface and formed anorthosite. Heavier minerals sank and produced the denser interior of the Moon. Anorthosite is an important rock type of the lunar highlands and probably formed the primitive lunar crust.

This sample has been determined to be 4. This date corresponds to the formation of a large lunar impact basin from which the rock was thrown. Other studies indicate that the rock lay exposed on the lunar surface for 8. Lunar breccias are rocks produced by the smashing, melting, and mixing of the lunar surface materials by large and small meteoric impacts. Evidence of this process can be seen in the countless craters of various sizes which cover the Moon.

The Crisium basin, about kilometers miles in diameter is one of many large circular lunar depressions. These basins or craters formed by the collisions of very large meteoroids with the Moon. After the impacts, basalts from the interior of the Moon welled up and partially filled the basins.

Material thrown out by the impacts that produced the basins is spread widely over the Moon. This crater in Mare Imbrium, 32 kilometers 20 miles in diameter, is surrounded by a blanket of material blasted out by the impact that produced the crater.

Near the crater's rim the ejected material is thick and hilly. Farther away, the material is thinner and has a radial pattern. Rocks thrown out during the formation of large impact craters often produce smaller, secondary craters when they fall back to the lunar surface. The meter foot secondary craters in the foreground of this photograph have numerous rocks on their rims.

These rocks were excavated from beneath the surface by the impacts. Tiny impact craters, called "zap pits" are produced by small, high velocity particles and are common on the exposed faces of lunar rocks. Some rock fragments found in breccias are pieces of more ancient breccias. Repeated impacts have smashed the older rock and re-fused it with more recently formed breccia. As many as four generations of breccia have been found in a single lunar rock.

Regolith is the loose, dusty soil that covers the Moon's surface up to a few meters on the Mare and sometimes triple that on the Highlands. It exists due to the Moon's constant bombardment with meteors - as the first line of defense, what might be larger rocks are ground into a powder upon these impacts. The composition of the Regolith mirrors that of the rocks underneath, which means the soil is mostly basalt on the the Mare and largely Highland rock on the Highlands.

What rock types are most common on the moon? Becca M. Feb 4, Breccia: Shocked Rock Breccia are composite rocks formed from jagged and irregularly-shaped fragments that melted and then fused together during a meteoric collision.

Highland Rock: Anorthosite Anorthosite is found across the Moon's lunar highlands and likely formed the primitive lunar crust. Related questions Is there evidence for water on the moon? What are the lunar regolith?