The Apollo lunar landings yielded an abundance of new scientific data on the Moon. The various experiments placed on the surface provided information on seismic, gravitational, and other lunar characteristics. But perhaps the most dramatic result of the missions was returning a total of more than 800 pounds of lunar rock and soil for analysis on Earth. These samples of the Moon offered a deeper appreciation of the evolution of our nearest planetary neighbor.
Lunar surface basalts are believed to have their origins in partially melted areas 100-400 kilometers (60-250 miles) beneath the large meteoroid impact basins. The basaltic material welled up into the basins through cracks created by the impacts. The basalt flows covered areas up to 1200 kilometers (750 miles) away from where they had arisen.
Basalt (shown in pink) is not distributed uniformly over the Moon. Nearly 26% of the near side of the Moon is basalt and only 2% of the far side is basalt. Most basalt in either hemisphere is found in areas of lowest elevation, particularly in the very large impact basins.
Distinct basalt flows overlap each other near a wrinkle ridge in Mare Imbrium. These lava flows are about 35 meters (115 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 4.19 billion years old by the Argon method of dating. 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 8.6 million years after it was moved again by the formation of Spook crater.
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 700 kilometers (430 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 1-3-meter (3-10-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. This zap pit is 50 microns (2/1000 inch) in diameter and has a raised rim of glassy material caused by the impact.
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.
A common feature of many lunar crystalline rocks is the grinding and crushing, or granulation, of their minerals caused by repeated meteoric bombardment. This makes the original textures difficult to recognize.
A glassy material produced by the shock of a meteoric impact coats this rock fragment from an Apollo 11 breccia sample. Since the glass is not uniform in composition, it strongly indicates that the glass was formed by shock.
This ellipsoidal lunar glass particle contains numerous tiny spheres of nickel-iron. These metallic spheres are meteoric in origin and indicate that the glassy particle was produced by shock melting during a meteoric impact.
Lunar breccias are fragmental rocks which are the products of meteoroid impacts. This sample is a type called lithified mature soil. The sample consists of fragments of glass, minerals, and rock cemented together in a glassy matrix. The materials which compose this sample have been determined to be 4.53 billion years old by the Rubidium-Strontium method of dating.
Apollo 17 astronauts discovered an area of orange soil on the rim of Shorty crater, in the Valley of Taurus-Littrow. A trench was dug to obtain samples of this material. Subsequent study of the orange soil indicates that it was formed during volcanic eruptions 3.7 billion years ago.
Lunar soil contains fragments of the major lunar rock types: basalt (A), anorthosite (B), and breccia (C). In addition, round glass particles (D) are common. The fragments that make up lunar soil are the products of the ceaseless bombardment of the Moon by meteoroids which smash and grind rocks into soil and weld soil into new rocks.
The texture of undisturbed lunar soil can be seen in this close-up photograph, which shows the soil enlarged about 35 times. This soil is composed of aggregates, clumps of small particles 0.1-0.6 millimeters (4/1000-24/1000 inch) in diameter.
Most lunar glassy materials were created by the shock of meteoroid impacts. However, the green glass particles shown here probably had a different origin. The uniformity of their size and composition suggests that they were formed in lava fountain eruptions.
Orange glass spheres, like the green glass spheres, originated in lava fountains. The glass in the spheres shown here has begun to crystallize into dark, needlelike crystals.
Lunar soil consists of particles of many sizes. Here individual particles less than 1 millimeter (4/100 inch) have been picked from the bulk soil and segregated by type.