Mingled lunar breccias
Breccias that mix highland and mare rock, from the borders between the two.
- Classification
- Stony meteorites › Achondrites › Planetary achondrites › Lunar meteorites › Mingled lunar breccias
- In our catalogue
- 3 meteorites
- Heaviest
- Northwest Africa 2727, 191 g
Mingled breccias contain both pale highland material and dark mare basalt, stirred together by impacts. They probably come from places near the edges of the maria, where the two kinds of terrain meet.
Mineralogy and chemistry
Mingled breccias combine anorthite-rich highland fragments with pyroxene-rich basalt fragments and glass, cemented by impact. Their bulk iron content falls between the two end members, typically about 8% to 15% iron oxide. Some contain the KREEP component, rich in potassium, rare-earth elements, phosphorus and thorium, suggesting a source near the Procellarum region of the near side, where KREEP is concentrated.
Origin and formation
Wherever the maria meet the highlands, impacts mix material from both. Lunar soil at such boundaries becomes a mixture, and later impacts compact and weld it into breccias. Mingled breccias therefore come from contact zones and help map how mare basalt and highland crust are distributed. The varying proportions of the two rock types in different meteorites, and their cosmic-ray exposure histories, show that they come from several separate launch sites.
Abundance and famous examples
They are a small but significant fraction of lunar meteorites. Calcalong Creek, a small stone of about 19 g found in Western Australia, was the first lunar meteorite recognised from outside Antarctica; although catalogued as anorthositic, it carries a mixture of highland, mare and KREEP-rich material. Several Antarctic and north-west African stones are also classed as mingled, and catalogue classifications such as 'basalt/anorthosite' breccia describe the same kind of rock.
Why they matter
Mingled breccias show how vigorously the lunar surface has been stirred. Their glass beads and solar-wind gases record exposure at the surface, and the different ages of the fragments inside one stone record several impact events. Comparing their chemistry with orbital maps of the Moon's surface has helped narrow down the regions they came from.
Lunar meteorites of every kind are rare: all the Moon rock on Earth, including the samples returned by missions, amounts to only a few tonnes. They should be bought only with a recognised classification, and finds in deserts are subject to the law of the country where they lie.
How to recognise one
A mingled breccia shows both white and dark grey to black fragments in a fine matrix, often with a thin fusion crust. It is weakly magnetic. As with all lunar meteorites, only laboratory analysis can confirm one.
Famous examples
- Calcalong Creek Lunar (anorth), Australia, 1960 · 19 g
Related groups
- Feldspathic lunar meteorites Pale breccias from the ancient lunar highlands, the most common kind of Moon rock to reach Earth.
- Lunar basalts and gabbros Dark volcanic rock from the lunar maria, the Moon's great lava plains.
- Howardites Broken rubble from the surface of asteroid Vesta, mixing crust and mantle rocks.
- Lunar meteorites Rocks from the Moon, found mainly in deserts and Antarctica.
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