An Article In Meteorite-Times Magazine
by Tom Phillips and Norbert Classen
As you may of noticed, Norbert Classen is a
planetary meteorite collector and fan. Actually, he goes way beyond
just collecting! He has been adding to my planetary meteorite image
write ups with sample photos and interesting descriptions. This
month however, I wanted to talk about Bilanga which is a diogenite
and not planetary. Norbert came through again!
I was wondering if he would have a sample to photograph, and of course he did! This is his sample and his description.
Nearly ten years ago, on October 27th, 1999, a large meteorite shower was witnessed to fall in the villages of Bilanga-Yanga and Gomposago, Burkina-Faso, Africa. The locals heard several loud explosions, but opposed to some reports, they obviously didn't witness the initial fireball as the sky was obscured by clouds that day. According to Mike Farmer and Bob Haag, who went to the fall site in early 2000 to buy pieces of the Bilanga fall, the locals only saw many stones raining down over a large area of scrub bush land surrounding the villages after hearing the sonic booms.
Farmer, Haag, and several other dealers secured more than 25 kg of meteorites with fresh black fusion crust in Bilanga-Yanga, and made them available to institutions, scientists, and private collectors. The Bilanga meteorite was later studied by Dr. Addi Bischoff, University of Muenster, Germany, and classified as a rare monomict diogenite breccia, mainly composed of orthopyroxene, and minor diopside, plagioclase, chromite, troilite, and silica. In one specimen a single grain of native copper has been observed - a first for HEDO meteorites which are thought to have their origin on asteroid Vesta, one of the largest objects in the main belt which shares a lot of features with the terrestrial planets Earth, Mercury, and Venus.
My own collection sample is a 2.60g slice with dimensions of about 31x19x1.8mm, and I originally purchased it from Dieter Heinlein who obtained about 4 kg of the Bilanga fall. It shows the typical light-clored matrix of Bilanga with the larger brownish-green orthopyroxene clasts, small black chromites, a few tiny shock veins, and a single white plagioclase clast. It's a wonderful and fresh example of this neat diogenite, even though it has no fusion crust.
The thin section came from Jeff Hodges. Jeff is a perfectionist with the thin sections he has made. The quality of the thin section made my work a lot easier.
I just got a new toy. A Shinko polimeter and I wanted to share a series of images showing the thin section in rotation. The color change is beautiful. The images are in close up but no magnification was used. I did use a full wave retardation plate (tint plate) at 28 degrees off of full extinction. The plate was used to draw out color extremes as well as to control exposure contrast issues. Each rotation is 10 degrees and I completed the full circle (even though after 180 degrees it is redundant) to give an idea of how colors change in rotation and to show how I get some of the intense colors often seen in my high magnification images.
This is the polarimeter. I should point out this is an improvised use for this equipment. You can see by the PVC stage I am using!
Now for some microscope shots. This set was taken with a Field of view (FOV) of 2.30 mm.
FOV 0.95 mm.
FOV 0.40 mm.
FOV 0.25 mm.
Let me know if you enjoyed the polarimeter rotation shots and I will try to include some more in the future.
Be sure to visit Norbert Classen's site at:
Tom Phillips can be reached by email at:
The Tom Phillips Microscopic Meteorite Photography and Gallery