ORIENTED METEORITES

Written By Aubrey Whymark 2007-2017
What happens to meteorites when they pass through the Earth's atmosphere and can any comparisons be drawn with tektites?

Radial Flow Lines

Different meteorites, composed of different material, behave in different ways. Perhaps the most spectacular oriented meteorites with flow lines are the achondrites. Eucrites such as Millbillillie and Camel Donga are amazing. Some Martian meteorites also have spectalular flow lines (and a price to match!)
 
ABOVE: A bullet Sikhote Alin. Note the 360 degree radial flow lines. The point from which these flow lines radiate is known as the stagnation point. Exceptionally well preserved australite buttons also show radial flow lines. Anda tektites also appear to have a stagnation point from which the texture radiates, however, these form by a totally different mechanism.
ABOVE: An oriented NWA meteorite. The posterior surface shows a rollover lip, where melt from the front of the specimen cooled on the on the back. The flanges on Australite buttons formed in a similar manner.

Polygonal Cracking

As a rock cools, it takes up less space and contracts. This results in polygonal cracks. We commonly see polygonal cracks in igneous rocks and also in breadcrust tektites from the Philippines.
 
ABOVE: Regmaglypts developed on an LL Chondrite from NWA. Australite buttons also show turbulent flow features and the anterior margin.
ABOVE: Fusion crust showing contraction cracks on an ordinary chondrite from NWA.
ABOVE: An Australite button showing radial flow lines and turbulent flow.