28 Oct 2010

(Please click images to enlarge)

Space Rocks on Earth (Meteorites)

What is a meteorite?

Well, little bits of rock and dust are always floating around space, and sometimes our planet passes through debris left behind from comets travelling through the system. A meteor is one of these little bits of dust/rock that falls into the atmosphere, usually leaving a hot trail as burns up (most 'shooting stars' are actually dust only a few millimeters across!)

The meteroid (as it is know as before it enters the atmosphere) is heated by passing through the atmosphere, 'so that it glows and creates a shining trail of gases and melted meteoroid particles'. Sometimes the fragments are large enough to make larger fireballs. Most burn up before they reach the ground, and some have been known to have exploded in the air causing great devastation, eg Tunguska :

However, occassionally a meteor will impact with the ground, at which point it is called a meteorite, rather than a meteor. Sometimes the fragements are enormous, and sometimes they're tiny. What they are made of can often tell us where they come from (asteroid, comet, another planet or the moon, perhaps), but the most fascinating thing (especially when you have a piece of one in your hand!) is that they all come from space!!

Recently, Mr Pert and I attended a kind of space conference for schools, where one of the talks was on meteorites. The talk was fascinating, and we thought it would be really cool to have some meteorite samples of our own. Over this last holiday, I had a look on e-bay, and found a UK reputable seller of meteorites, British Jurassic Fossils, and purchased three little ones to start off our collection:

Here is a little about each of them (more information available with the samples and on the internet):

This first sample is from Gran Chaco Gualamba, Chaco, Argentina. It is of Iron: Octahedrite, coarse (3.0mm),and was from a meteorite first found 1572. According to Wikipedia, the crater field was 20km by 3km and consisted of 'at least 26 different craters' The way the crater field covers the ground indicates the meteorite must have broken up as it fell through the atmosphere and each of the shattered pieces created their own impact.
This is the Las Viboras fragment:

The biggest of the craters was about 115×91 meters (if you think of the 100m running track, it's a little longer than that, and nearly as wide!) Smaller fragments of the meteorite were found up to 60km further away...
It has been estimated that the main fragment was about 4m in diameter..
our little piece is much smaller, but will have the same history:


Stone chondrite meteorite, unclassified

Many ordinary chondrites are being found in North West African , . So many researchers don't have the time to classify all of them coming out. This specimen is un classified.

This meteorite could be just packed with inclusions and , chondrules, armored chondrules, shock veins and more showing in the specimens. In addition, an important point to note is that this meteorite is very stable and can be easily displayed.

Mundrabilla Iron Meteorite

This is one is best described by the seller, British Jurassic Fossils:

The first pieces of the Mundrabilla [Western Australia] meteorite were found in 1911. In March of 1966, two large masses of about 8 and 11 tons were found by geologists R. Wison and A. Cooney and described under the name Mundrabilla. In 1979, two more large masses weighing totaling about 1640 kilograms were found about 20 km east of the 1966 location.

Mundrabilla has a very low iridium content and very high troilite content and is designated an anomalous iron. The troilite is present in small nodules accounting for up to 35 % of the volume of the meteorite. The "knuckle-shape" of many individuals is a result of the selective ablation of troilite during atmospheric entry leaving knobby taenite crystals.

Nantan Meteorite

And finally, due to the kindness of British Jurassic Fossils, who donated this wonderful specimen to the school, we have a great, feel-in-your-hand Nantan meteorite. This, I believe is an Nickel-Iron meteorite (hopefully more details to follow...)

Meteorite Fans: If you can't wait until these meteorite samples are shown in one of your classes, please feel free to come and see me in the prep room opposite Lab 8, and (if I have time) you might be allowed a sneak preview!

Teachers in other departments: please feel free to order them for a lesson! Hopefully, we might have a few more over time.. (I believe Mrs O'Grady, geography department, also has a sample of tektite (a piece of Earth rock that has been projectiled into space when a meteorite impacted the ground, and which shows many of the characteristics of meteorites (ultra-heated, has been in space), but consists of material from Earth)...Please remember to see if any of your A level class has a write-ups of the impact lesson we can use :-)

**If anyone has any samples of their own they'd like to donate to the school, we would welcome them to our new collection! And if anyone has any boxes we can display the samples in, they would also be great! [Thanks in advance :-) ]

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