Spinel

 

Spinel, a metal oxide, is the second most abundant oxide mineral on Luna.

Abundance and distribution

• Spinels have been found in all Lunar mare basalt and some highland samples. (Lunar Sourcebook, 146)
• In fact, spinels make up as much as 10% of the volume of some basalts (Apollo 12 and 15). (Lunar Sourcebook, 143)
• Spinels are the second most abundant opaque material on Luna. (1, pg 143)
• Most abundant in mare basalts but can occur in highland anorthosites, anorthositic gabbros, troctolites, and impact mixtures of these materials. (1, pg 146)
• Often found with ilmenite and native metallic iron. (1, pg 147)

 

Physical properties

• Magnetic = I looked and couldn’t find any info. I’ll keep looking.

 

Chemical composition

• Spinels are a complex mixture of ulvöspinel (Fe₂TiO₄), chromite (FeCr₂O₄), hercynite (FeAl₂O₄), picrochromite (MgCr₂O₄), spinel (MgAl₂O₄), and MgTi₂O₄. Spinels are hard to categorize as they can substitute their most common elements for many other minor and trace elements. (2, Chapter X,M)
• Spinel chemical composition varies quite a bit between sites and between samples from the same site (Lunar Sourcebook, 145).
• Some spinels contain magnesium instead of iron but most Lunar spinels are iron-rich (Lunar Sourcebook, 145).
• The spinels that we are after (for the iron at least) are ulvöspinel (Fe₂TiO₄), hercynite (FeAl₂O₄), and chromite (FeCr₂O₄).  All of these can be present in the same sample, including spinels with magnesium, so we need to be prepared to deal with each one.

 

Mechanical separation

Not needed for this phase of the project.

 

Refining

Not needed for this phase of the project.

 

Data

Analysis of spinel from rocks and soils (selected samples)(Lunar Sourcebook, 173-175)

• Apollo 11 (Low-K)(<0.11% K₂O)
  • Iron oxide (FeO) by weight percent range: 42.1% – 65,.7%
  • Average FeO by percent weight = 51.4%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.85 – 1.00
• Apollo 12 olivine (>10% MgO, <5% TiO₂)(Low-Ti)(1.5-9% TiO₂)

• • Iron oxide (FeO) by weight percent range: 26.8% – 57.4%
  • Average FeO by percent weight = 48.68%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.66 – 0.98
• Apollo 12 pigeonite [a form of pyroxene] (<10% MgO, <5% TiO₂) (Low-Ti)(1.5-9% TiO₂)
  • Iron oxide (FeO) by weight percent range: 26.3% – 63.3%
  • Average FeO by percent weight = 52.40%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.66 – 1.00
• Apollo 12 ilmenite (<10%MgO, >5% TiO₂)(Low-Ti)(1.5-9% TiO₂)
  • Iron oxide (FeO) by weight percent range: 33.3% – 51.6%
  • Average FeO by percent weight = 49.43%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.81 – 0.92
• Apollo 14 (Aluminous, Low-Ti)(>10% Al₂O₃, 2-5% TiO₂)
  • Iron oxide (FeO) by weight percent range: 29.24% – 48.33%
  • Average FeO by percent weight = 40.36%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.73 – 0.97
• Apollo 15 pigeonite [a form of pyroxene] (<10% MgO, <5% TiO₂) (Low-Ti)(1.5-9% TiO₂)
  • Iron oxide (FeO) by weight percent range: 24.38% – 26.38%
  • Average FeO by percent weight = 25.38%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.65 – 0.71
• Apollo 15 olivine (>10% MgO, <5% TiO₂)(Low-Ti)(1.5-9% TiO₂)
  • Iron oxide (FeO) by weight percent range: 34.35% – 61.42%
  • Average FeO by percent weight = 46.67%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.85 – 0.99
• Luna 16 soil (unknown rock types)
  • Iron oxide (FeO) by weight percent range: 25.33% – 37.81%
  • Average FeO by percent weight = 30.08%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.67 – 0.95
• Luna 16 (Aluminous, Low-Ti)(>10% Al₂O₃, 2-5% TiO₂)
  • Iron oxide (FeO) by weight percent range: 50.07% – 60.04%
  • Average FeO by percent weight = 55.01%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.94 – 1.00
• Luna 20 soil (unknown rock types)
  • Iron oxide (FeO) by weight percent range: 10.70% – 35.70%
  • Average FeO by percent weight = 24.08%
  • Ratio of iron to magnesium [Fe/(Fe+Mg)] range = 0.22 – 0.81

 

Resources

1. Lunar Sourcebook
2. Extraterrestrial Materials Processing and Construction