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Al Mahbas (Pallasite) - 5.63g Half Individual
with 'Rainbow' Olivine caused by "Schiller Effect".

Al Mahbas was discovered in Western Sahara during 2004. This specimen was retrieved by Mike Farmer on expedition into the area from November 27th - December 3rd, 2004. Al Mahbas is a Pallasite meteorite composing olivine crystals in a matrix of metallic iron/nickel and has a Total Known Weight around 3 kilograms. In the case of Al Mahbas the metal has weathered into a 'shale' form while the majority of the olivine crystals are still relatively unweathered.

In the specimen below it is obvious that at least one of the olivine crystals has undergone a dramatic change. One main crystal (centre right) has a strong coloured 'rainbow' effect while at least one or two more towards the left have the beginnings of the same feature. The only way to describe what it looks like close-up, would be to say it 'looks' like Opal. It appears to be a prismatic effect with light being separated within the crystal. The centre of the main olivine starts with a purple colour and graduates outwards through the spectrum but again finishes with a blue/purple colour around the edge.

The images below barely show it but deep within at least one or two of the crystals towards the left side is the same effect. Albeit to a lesser degree. The negative view images help to distinguish and show the different regions. The final False Colour View helps highlight the areas in which the feature is found or starting to form. The green will particularly assist in highlighting these areas.

This feature is not a result of photographic aberration or an effect of the specimen's preparation. More likely it is from what is known as the 'Schiller effect' or some other form of mineralogical alteration possibly due to weathering. The iridescence or 'Schiller effect' can be caused by the scattering of light between thin, platelike layers within the crystalline structure or rather, a result of "interference patterns set up by crystal twinning, the regular exsolution of other mineral phases, or other systematically arrayed inclusions in the crystal lattice". This is the same effect which can be seen in some opals. Very interesting and unique either way! This piece is part of the Meteorites Australia Collection. (MA.04.0129)

Al Mahbas (Pallasite) - 5.63g Half Individual.

'Rainbow' olivine crystals. (close-up through 10X loupe)

'Rainbow' olivine crystals - Negative view. (close-up through 10X loupe)

'Rainbow' olivine crystals. (close-up through 10X loupe)

'Rainbow' olivine crystals - Negative view. (close-up through 10X loupe)

'Rainbow' olivine crystals - False colour view. (close-up through 10X loupe)



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