Meteorites: up close and personal (in your hands)

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Meteorites: up close and personal (in your hands)
Posted by chipdatajeffB on Saturday, July 26, 2008 11:54 AM

It's been a while since I posted anything on meteorites. Today I'm getting my Meteorite Petting Zoo organized for a display at the Texas Astronomical Society's upcoming (Sept. 6th) observance of Astronomy Day.

Part of that process was deciding how best to display thin sections so the public can "see inside" a meteorite. The image below is the best of a series I made this morning using a newer, simpler technique which does not require a microscope.

This is what's called a petrographic thin section, which is essentially a paper-thin (30-micron) slice of rock mounted to a glass microscope slide. In this case, the rock is a piece of the meteorite named Vaca Muerta (Spanish for "dead cow"). It's a mesosiderite and the longest dimension of this particular slice is just under 20mm.

The colors are formed by cross-polarized light. Light from a flash unit passes through a polarizing filter beneath the thin section, through the crystals in the thin section, and then through another polarizing filter between the camera and the thin section. As you rotate one of the polarizers, you can position them so that no light at all passes through the polarizing filter "sandwich" except that which has been "modified" by passing through the crystals in the meteorite. I think the sandwich will make a nice display when laid out on a small light table (you can see the thin section exactly as it appears here except it will be a bit smaller.

The colors, and the way the light changes as it passes through a crystal, can tell you what mineral is present. The appearance of cracks and/or cleavage planes in the crystal can tell you something about whether the meteorite was remelted after initial formation, or whether it was shocked by an impact.

And, as well, the polarized light makes for simple, pretty pictures ... Smile,Wink, & Grin

Other examples, including macros as well as micrographs, are in my Meteorite Thin Sections set at Flickr!.

Update: I got the substage raise/lower mechanism on the Illumitran fixed, so it's much easier to do this now. Here's a new thin section (just got it this week) of the Allende meteorite:

Nice chondrules in there, some look like miniature "distant Earths" ...

 

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

www.3rf.org

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Posted by chipdatajeffB on Tuesday, July 29, 2008 12:42 PM

And here's the setup:

The Illumitran is an '80s-era slide copier. It has a focusing lamp and an electronic strobe in the base. The large knob at lower left is the raise/lower mechanism that raises the substage up under the flat stage where you put the slide (or, in this case, petrographic thin section -- the meteorite) to be copied.

A standard camera bellows is attached to the vertical pillar and rack and pinion adjustments allow you to raise/lower the enlarger lens and camera mount independently. This means you can adjust the macro magnification from about 1:1 to about 1:4, with this particular lens.

You can do this yourself (assuming you have a camera with a macro lens and a thin section) with a simple light table (tracing table) and two linear polarizing filters. If you bought that stuff new, it would cost you about $80 (not including camera and thin section). Thin sections run from about $15 to $300, depending on the dealer, the quality, and the particular meteorite. Most of mine cost between $35 and $70.

You simply make a "sandwich" of the polarizers, rotating one of them 90 degrees relative to the other to block out the light in the field surrounding the thin section, and put the thin section between the filters. Place the sandwich on the light source and shoot the photo with the camera suspended over the thin section (in macro mode).

The Allende image in the previous post is a 1:1 macro. The large chondrule at lower left is 2mm actual diameter and is 125 pixels wide in the image. The camera sensor has 127 pixels per mm, so this is almost exactly 1:1 scale. The Vaca Muerta image is more like 1:2 scale.

In the setup photo, a film camera is standing in for my DSLR, which I used to make the setup photo.

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

www.3rf.org

  • Member since
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Posted by cousin it on Sunday, August 03, 2008 2:49 PM

 Wow! This brings back memories of my days as an undergrad. Quick question; are the dark areas in the first image from amorphous minerals, or areas that have been phased out, or ???

"I'm willing to be open-minded, but not so open-minded my brains fall out."- Chipdatajeff
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Posted by chipdatajeffB on Monday, August 04, 2008 12:01 PM

That is called the matrix. It's composition differs by meteorite "clan" and petrologic type. A more heavily-weatherd meteorite will experience a change in the matrix material.

So, for example, a mesosiderite may fall to Earth with a matrix that is composed of crushed silicate crystals and nickel-iron. Once it sits on the Earth's surface for a while, weathering will oxidize the iron into a form called troilite. Over a longer time, the troilite and remaining iron will change to hematite.

There's lots of variability, again depending on the original material and the amount of weathering.

A heavily shocked meteorite (such as a mesosiderite -- formed by the collision of two asteroids) is more easily weathered because water can get inside via the shock veins.

Some matrices are more fine-grained and homogenous, but most of the thin sections I've actually studied show a fair degree of mixing among silicates and metals.

A brecciated meteorite (there are some thin-section examples in my Flickr! albums) is by definition a more xenolithic type (xeno meaning "foreign" and lithic meaning "rock"), so a specimen can be practically all matrix.

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

www.3rf.org

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Posted by chipdatajeffB on Monday, September 16, 2013 10:47 AM

I see it's been about 5 years since this thread was last updated. The news is that about a month ago a blogger happened upon my Flickr! album of meteorite thin-section photos made in cross-polarized light and while not exactly going viral those photos have been viewed by thousands of people around the world.

My Flickr! albums, all told, average fewer than a hundred hits a day. For a period of a few weeks after the initial blog, they experienced thousands of hits per day, topping at over 30,000 hits on one particularly busy day -- most of this activity related to the100-odd thin-section photos.

Publications included London's Daily Mail, The Huffington Post, Fast Company Magazine's CoDesign pages, The Weather Channel, Gizmodo ... and thousands of individual bloggers.

The point here is not that my photos are that great.

It's that something as esoteric (weird?) as the insides of a meteorite can be interesting to such a large number of people of different interests. The Fast Company article was not one of their typical "business" articles ... it was on the part of their site that interests graphic designers. I find that both odd and enlightening. It shows that artistic inspiration can come from practically anywhere.

I like to think of meteorite thin sections as the "insides" of "outer space." I knew that kids are fascinated by "space rocks" ... but I never dreamt that there was such a wide audience for snapshots of them!

Who knew?

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

www.3rf.org

  • Member since
    November, 2012
Posted by MooseMan01 on Monday, September 16, 2013 10:08 PM

That's great. I've enjoyed reading your meteorite threads such as this one. Maybe the sudden interest stems from the recent explosion of the meteor over Russia, and scientific efforts to catalog near earth objects. In any case, public interest in real science such as this can only be a good thing!

  • Member since
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  • From: Southern California near Disneyland
Posted by Silveradogold on Friday, October 11, 2013 12:23 PM

Thank you chipdatajeffB,

The pictures are awesome ! I really like the microscopic and macroscopic world as well as astronomy. It is kind of you to share the wonders of the natural world with others.

Clear Skies ----- Silveradogold Cool

 

33° 48' 10"N, 117° 57' 49"W "Remember, without data your conclusion is just another opinion" Look at all the stars. You look up and you think, "God made all this and He remembered to make a little speck like me." It's kind of flattering, really. +++ 150mm SkyWatcher refractor - 120mm reflector - Celestron SkyMaster 15x70mm Binoculars +++

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