How do lunar rock samples differ from Earth rocks and what tests confirm their origin?

1. Mineralogy and dominant rock types: what the Moon is made of

The Moon’s surface is largely igneous: the dark maria are basaltic and made mostly of pyroxene, plagioclase and olivine, while the highlands are dominated by anorthosite — nearly pure plagioclase feldspar — reflecting a crust formed from a solidified magma ocean ^{[1] [5] [4]}. Many lunar rocks are breccias and impact melts that record bombardment processes rather than weathering or sedimentary recycling common on Earth ^{[5] [1]}.

2. Bulk chemistry and compositional fingerprints

Lunar rocks show narrower SiO2 variation than Earth rocks because the major lunar minerals have similar silica contents, and they tend to be low in volatile alkali elements and sulfide-associated (chalcophile) elements compared with terrestrial rocks and most meteorites — a recurring, diagnostic chemical pattern ^{[6] [3]}. Mare basalts often contain higher Fe and Ti in pyroxenes and oxides than many terrestrial basalts, with TiO2 reaching several weight percent in some lunar basalts — a compositional clue used in classification ^{[7] [2]}.

3. Redox state, water and iron oxidation: anhydrous and largely ferrous

A striking difference is the Moon’s anhydrous nature and the near absence of ferric iron (Fe3+) in bulk lunar samples: most iron is present as Fe2+, unlike many terrestrial rocks that commonly show Fe3+-bearing minerals formed in the presence of oxygen and water ^{[2] [7]}. This reduced, dry chemistry is a powerful discriminator between lunar material and typical Earth rocks or many meteorites ^{[2] [3]}.

4. Textures and regolith features that scream “airless body”

Lunar soil (regolith) contains agglutinates — mineral fragments welded by glass formed from micrometeorite impacts — as well as glass spherules, vesicle-bearing pyroclastic glasses, and “zap pits” from solar wind and micrometeorite bombardment; these microtextures are uncommon in Earth rocks and record the Moon’s lack of atmosphere and surface gardening by impacts ^{[5] [4] [8]}. Many returned rocks also contain shock-produced glass veins and impact melt breccias diagnostic of high-velocity collisions on the Moon ^{[4] [5]}.

5. Tests and measurements used to confirm lunar origin

Provenance is established through a combination of methods: mineralogical identification (e.g., anorthosite or mare basalt assemblages) and microtextures (agglutinates, glass), bulk and trace-element geochemistry showing low volatiles/alkalis and chalcophile depletion, distinctive Fe–Ti oxide and pyroxene compositions, rare-earth element patterns, and isotopic ratios — especially high-precision oxygen isotopes — compared to Apollo reference collections ^{[3] [7] [1] [9]}. Additional lines include lack of terrestrial weathering signatures (for Apollo-controlled samples), cosmogenic exposure ages consistent with lunar ejection for lunar meteorites, and matching glass and shock features to known lunar impact processes ^{[3] [5]}.

6. Limits, ambiguity and how claims are vetted

Identification is robust when multiple, independent tests agree, but caveats remain: lunar meteorites can be Earth-weathered and some terrestrial rocks superficially resemble lunar compositions, so single tests (like a handheld XRF) are insufficient for proof; laboratories compare unknowns to the Apollo/Luna “library” and use trace and isotopic fingerprints to reach a confident assignment ^{[3] [4]}. Recent high-precision oxygen isotope work has even revealed subtle differences among lunar rock types and between deep lunar mantle samples and Earth, showing that isotopic diagnostics continue to evolve and sometimes refine origin models rather than offering a single, static test ^{[9] [10]}.