Lodranites
Coarse-grained leftovers after melt drained away.
- Classification
- Stony meteorites › Achondrites › Primitive achondrites › Lodranites
- Share of witnessed falls
- about 0.1%
- In our catalogue
- 50 meteorites, 1 seen to fall
- Heaviest
- Northwest Africa 4933, 2.53 kg
- Earliest recorded fall
- Lodran, 1868
- Type specimen
- Lodran, fell in Pakistan in 1868
Named after Lodran in Pakistan, which fell in 1868, lodranites are coarser-grained than acapulcoites and are depleted in plagioclase and troilite. They are residues: rock left behind after partial melts drained out. Acapulcoites and lodranites share oxygen isotopes and come from the same asteroid.
Mineralogy and chemistry
Lodranites are coarser than acapulcoites, with grains about 0.5 to 1 mm across, and are made mainly of olivine, orthopyroxene, iron-nickel metal and troilite. Plagioclase and calcium-rich pyroxene, the minerals that go into the first basaltic melt, are scarce or missing, and troilite is often depleted as well. Some lodranites are unusually rich in metal; Lodran itself contains roughly equal amounts of metal and silicates.
Their olivine and pyroxene are poor in iron and in some stones show reverse zoning, with iron decreasing towards the rims, a sign that reactions with carbon or other reducing agents removed iron as the rocks were heated. Oxygen isotopes are the same as in acapulcoites.
Parent body and formation
Lodranites are residues. They were heated to roughly 1,150 to 1,250 °C, enough for a few per cent to perhaps a fifth of the rock to melt, and the basaltic and metal-sulphide liquids then drained away. What was left behind was a coarse, olivine and pyroxene-rich rock. The missing basaltic melt has not been found in any meteorite, so it may have erupted explosively into space or been lost when the parent body broke apart. Transitional stones such as Graves Nunataks 95209 contain veins of metal and melt caught in the act of draining.
Together with the acapulcoites, the lodranites form a continuous series from barely melted to strongly depleted rock. Laboratory experiments that heat chondrites reproduce this sequence, which helps scientists understand how melt separates in small bodies with weak gravity, where it is hard for liquid to escape.
Abundance, type specimen and famous examples
Lodran fell near Lodhran in the Punjab, in what is now Pakistan, on 1 October 1868; about 1 kg was recovered. It is the type specimen and still the only lodranite seen to fall. Several dozen more are known, all finds, many from Antarctica. Gibson from Western Australia and Graves Nunataks 95209 from Antarctica are among the better studied.
How to recognise one
Lodranites are coarse-grained, granular rocks in which greenish olivine and pyroxene crystals and bright metal can be seen with a hand lens. They are magnetic and fairly dense. With no chondrules and an igneous look, they are easily mistaken for terrestrial peridotite; only laboratory analysis can confirm one.
Famous examples
- Lodran Lodranite, Pakistan, 1868 · 1 kg
- Gibson Lodranite, Australia, 1991 · 67 g
- Graves Nunataks 95209 Lodranite, Antarctica, 1995 · 949 g
Related groups
- Acapulcoites Fine-grained rocks that only just began to melt.
- Primitive achondrites Rocks that began to melt but were never fully processed: halfway between chondrites and igneous rocks.
- Ureilites Carbon-rich rocks with diamonds, from an asteroid shattered by a giant impact. One was tracked in space before it hit Earth.
Photos shared under Creative Commons licences (Wikimedia Commons).