Source Review: Chemical Composition of Lunar Soil (Washington University)

Summary

Claim 1 — Seven major elements

Quote: "98-99% of the composition of lunar rocks and soil consists of seven elements: Oxygen (41-45%), silicon (Si), aluminum (Al), calcium (Ca), iron (Fe), magnesium (Mg), and titanium (Ti)."

Verdict: Consistent (q3.c1)

Why: Direct primary-source statement of the 41-45% O figure that anchors my regolith oxygen mass fraction derivation.

Claim 2 — Highland vs Mare mineralogy

Quote: "Highland samples (high Al2O3): dominated by plagioclase feldspar with strong Al-Ca correlation"; "Mare samples (low Al2O3): contain 'Al-poor, Fe-rich minerals pyroxene, olivine, and ilmenite'."

Verdict: Consistent (q3.c1, q3.c10)

Why: Standard mineralogical decomposition. Supports the q3.c10 framing that ilmenite is mare-specific.

Claim 3 — Titanium variability

Quote: "Titanium is the most highly variable major-element on the moon" — Ti concentrations "vary by a factor of 10 in lunar basalts."

Verdict: Novel supporting (q3.c10)

Why: Quantifies the Ti variability that drives mare-region ilmenite content variability. Strengthens the framing that ilmenite-reduction yield is site-specific within mare, not just mare-vs-highland.

Claim 4 — Mare composition figures

Quote: (from synthesis) Mare soils: FeO 15-17%, SiO2 40-48%, Al2O3 12-17%, CaO 10-13%.

Verdict: Consistent

Why: My pass-2 calc used FeO 18% (slightly high end of range), SiO2 45%, Al2O3 12%, CaO 11%. All within the canonical Apollo range.

Claim 5 — Highland composition figures

Quote: (from synthesis) Apollo 15 highland regolith: SiO2 45.1-46.6%, Al2O3 19.1-22.2%, FeO 5.58-8.25%, MgO 8.98-11.3%.

Verdict: Consistent

Why: My pass-2 calc highland (Al2O3 21, FeO 6, MgO 10) matches Apollo 15 mid-mafic highland regolith but is lower-Al than pure Apollo 16 anorthositic regolith (Al2O3 ~27, FeO ~5). Both are valid "highland" samples; my values are closer to the mid-mafic case. The 1% bulk O variation between the two is not load-bearing for q3.c1.

Chemical Composition of Lunar Soil — WUSTL Meteorite Site

bulk-composition

"98-99% of the composition of lunar rocks and soil consists of seven elements: Oxygen (41-45%), silicon (Si), aluminum (Al), calcium (Ca), iron (Fe), magnesium (Mg), and titanium (Ti)."

regional-mineralogy

• Highland samples (high Al2O3): dominated by plagioclase feldspar; strong Al-Ca correlation
• Mare samples (low Al2O3): contain "Al-poor, Fe-rich minerals pyroxene, olivine, and ilmenite"

titanium-variability

"Titanium is the most highly variable major-element on the moon" — Ti concentrations "vary by a factor of 10 in lunar basalts."

indicative-numbers-mare

(from web-search synthesis of LPI Lunar Sample Compendium 10082, 76565, etc.) Mare soils: FeO 15-17%, SiO2 40-48%, Al2O3 12-17%, CaO 10-13%, TiO2 highly variable (0.5 to 10%).

indicative-numbers-highland

(from Apollo 15 highland regolith samples and the Lunar Sourcebook ch.8) Highland regolith: SiO2 45.1-46.6%, Al2O3 19.1-22.2%, FeO 5.58-8.25%, MgO 8.98-11.3%, CaO ~13-16%, TiO2 <1%.

These are the canonical compositions I use as input to the calc pass.

isru-relevant-takeaway

For oxygen ISRU, every silicate phase contains ~40-45% oxygen by mass — so any whole-regolith process (MRE, carbothermal, FFC Cambridge) is feasible anywhere. Ilmenite-based hydrogen reduction is the high-yield route in mare regions where ilmenite is present at 5-15 vol%; it is uncompetitive in highland or polar regions where ilmenite is below 2 vol%.

For structural metals, Al is most abundant in highlands (anorthite), Fe is most abundant in mare basalt and ilmenite, Si is universal, Ti is mare-only and concentrated in ilmenite.