OSM 011a

OSM 011a

Classification led by Jen Mitchell

This meteorite belongs to Sean Mahoney and is comprised of 5 separate stones found near Oum El Assel in Algeria.

This meteorite will possibly receive an official name of 'Tindouf ***' - to be confirmed by the Nomenclature Committee of the Meteoritical Society.

The type specimen (21 g) will be on deposit at the University of Plymouth, along with a single, polished thin section.

On a later visit to the same site to search for more material, another 921g of smaller meteorite pieces were found buried. Initially they were believed to belong to the same fall, even though they differed visually. However, detailed analysis by the Space Rocks UK team found that the buried material is most likely an entirely different Eucrite, nicknamed OSM 011b.

BSE image of the OSM 011a eucrite breccia, with clasts outlined where possible. Heavy recrystallisation makes it difficult to find the boundaries between the different rock types.


Backscatter electron (BSE) imaging generates greyscale images based on atomic number contrasts - effectively measuring density. In geological samples, this technique shows the distribution of different minerals which we then combine with other techniques to give the elemental composition.

In the case of this meteorite, BSE imaging helped us identify a number of clasts (pieces of different types of rock that have been mixed together) by showing differences in textures. Meteorite breccias provide records of a wide range of rocks from asteroids and planets, letting us investigate a host of igneous and metamorphic processes that happened billions of years ago.

At the time of classification, we have identified at least three different types of eucrite stuck together in OSM 011a, each with different igneous histories. This meteorite is heavily recrystallised though, suggesting that this rock underwent a period of high temperature metamorphism on it's parent body before being ejected.

Compositional Analysis

Energy dispersive spectroscopy (EDS) provides the abundance of elements at a given point and/or across an area. This means that we can produce high-resolution compositional analysis of samples to work out exactly which minerals we're looking at and where they are.

OSM 011a is largely composed of low-Ca pyroxene, high-Ca pyroxene, and plagioclase. There are a number of accessory minerals including Fe-sulphides, chromite, Fe-metal, ilmenite, and silica - all of which are common in eucrites. Most importantly, the pyroxenes in OSM 011a suggest that this is a distinct meteorite from OSM 011b. Given that they were found on top of each other, this is very exciting!

Some meteorites gain new minerals when they land on Earth and sit outside for a long time before they are found and collected. This meteorite developed patches of baryte (a barium-sulphate) and titanium dioxide around its edges as a result of residing in a hot, dry environment for a significant length of time.

Combined Mg-Ca-Al element map of OSM 011a, overlain with accessory phases.

Red = low-Ca pyroxene; Green = high-Ca pyroxene; Turquoise = plagioclase; Pink = chromite; Purple = silica; White = ilmenite; Yellow = troilite

Meteorite Owners

Sean Mahoney

OuterSpacer Meteorites

Sean is a meteorite collector and dealer based in Spain, and a registered member of both the IMCA and GMA.

You can find out more about Sean's meteorite collection, OuterSpacer Meteorites, on his web page.

Gemma Thomas

Meteorite Girl UK

Gemma is a meteorite collector and dealer based in SW England, UK, and a registered member of the GMA.

You can find out more about Gemma's collection, Meteorite Girl UK, on her shop web page.