What should we know about meteorites?

Exhibition of meteorites in the Museum of Technology in Warsaw (2010)

SPACE within reach (0-1)

To see a World in a Grain of Sand
And A Heaven in a Wild Flower,
Hold Infinity in the palm of your hand
And Eternity in an Hour.
William Blake

SPACE within reach (0-2)

Sources: NASA, Internet

Fusion crust (1a)

When a meteoroid gets closer to the Earth its cosmic speed varies from 12 to 73 km/s. Then the stone comes across the atmosphere. The more the air gets thicker, the more it can slow down the intruder’s speed. The meteoroid heats up to 2500°C, and its surface is constantly melting. Some part of it evaporates and some is ‘blown away’ by the air speed and breaks away as drops that fall on the ground with the rain. Finally, the meteoroid slows down so much that it stops melting. This leaves glassy surface on the stone – the so called fusion crust. During this bumpy road through the atmosphere the stone loses up to 95% of its original weight!

Why is the crust black? It gets its color from iron compounds which can be found in most meteorites. However, there are some whose crust is glassy and of a milky-brown color such as moon meteorites (not rich in iron or not containing iron at all). The crust on a meteorite is like ‘enamel’ which protects it from hostile conditions on the Earth. The crust is usually 1 mm thick.

Illustration: Bassikounou, ordinary chondrite (photo: Tomasz Jakubowski)  •  NWA 482, lunar meteorite  •  Bensour, ordinary chondrite  •  Millbillillie, achondrite, eucrite  •  Sikhote-Alin, iron meteorite

Sources: Greg Hupe, Tomasz Jakubowski, Internet

See also: Skorupa obtopieniowa (fusion crust, fusion rind)

Regmaglypts and oriented meteorites (1b)

Regmaglypts is the name of characteristic surface as if someone left their fingerprints in clay. These were formed by air turbulences when a stone traveled through the atmosphere.
  What is interesting is that, the bigger the meteorite, the bigger its regmaglypts are. The size of one such 'fingerprint' can take from 1/8 to 1/10 of the stone. The most beautiful and visible regmaglypts can be found on iron meteorites. Sikhote-Alin is a really special one.
  When meteorites reach the surface of the Earth they have round shapes and if they do have any edges, they are smooth. It sometimes happens, however, that in the last phase of its fall meteoroid falls apart and there is no time for its fragments to get the melting. If so, the edges are sharp and the inside is bright.

It may also happen that during the fall a meteoroid does not rotate but flies like a bullet. As a consequence, we get oriented meteorites, such as Baszkówka. Its shape may look like a mashroom, a cone or it may have some less regular shapes. Still, we know the way it was falling. We can often see the so-called flow-lines on its front side. On the back, the air leaves a spongy kind of surface. Sometimes it may have a collar – the edge of melted material.
  Some meteorite showers consisted of many oriented meteorites as for intstance Gao-Guenie or Taza.

Illustration: photo: Svend Buhl  •  oriented meteorite Adamana

Sources: Svend Buhl, Internet

See also: Skorupa obtopieniowa (fusion crust, fusion rind)

Ordinary chondrites - the easiest to recognize (1c)

When we see a falling meteorite, there is 4 by 5 chances that it is an ordinary chondrite.
  Its name derives from a Greek word 'chondros' meaning 'seed'. And indeed, inside the stone we can see round seeds of silicate minerals olivine and pyroxene. Usually they are smaller than 1mm, but there are really big ones as well of several millimeters diameter. Among chondras we can see shining metallic iron with nickel and golden trolite.
  Chondrites can compose even 80% of a meteorite. The rest is the so-called matrix. If chondrites are well seen in the matrix, a meteorite is labeled with a digit '3', if they are less clear – 4, and those that can hardly be noticed are labeled with 5 or 6.
  But this is not the only problem. Ordinary chondrites come from different asteroids and this is what makes them different. Those having some coal in their matrix are called carbonaceous chondrites. If both, chondrites and matrix consist of enstantite, we call them enstatite chondrite. Most of falling meteorites, however, are oriented chondrites, such as Pultusk (the fall in Poland). They are further divided into 3 groups depending how much iron they contain. H (from 'high') means they contain a lot of iron, up to several per cent. Ordinary chondrites with the letter 'L' ('L' for 'low') contain a small amount of iron. The least amount of iron is labeledas 'LL' type.

Chondrites are like bricks forming the Solar System. Thanks to them we can get some information about the times before the Earth existed without any space travel.

Important. Sandstones also consist of round 'seeds', but this is quartz, not silicate mineral. What makes them also different is that sandstones do not contain metallic iron and sulfate minerals.

Illustrations: Chondrules in the fresh break of ordinary chondrite (photo: Jan Bartels)  •  Example of chondrules under a light microscope  •  Ordinary chondrite SaU 001  •  Ordinary chondrite NWA 5142  •  Chondrules in ordinary chondrite low type (photo: Tomasz Jakubowski)  •  Chondrules appearance under the polarizing microscope

Sources: Jan Bartels, Tomasz Jakubowski, John Kashuba, Tom Phillips, Internet

See also: Chondry (chondrules) • Quiz – zgadnij jaki to typ chondry? (“Chondrules” – a quiz)

Asteroid belt (2b)

There are a few thousands of asteroids between Mars and Jupiter’s orbits. Most of meteorites originate from there. These asteroids were created milliards years ago, and very strong gravitational Jupiter forces did not let them form clusters to create a planet. Meanwhile, the asteroids were undergoing a variety of geological processes and their mineral compositions were thus modified. As a result, some of them have iron inner core, in others olivine mantle and basalts shells can be discovered.
  But this is not the end of their interesting story. Because there is a quite a big number of them, collisions happen quite frequently. Very often smaller and bigger rock pieces are falling apart and fly to the space. Sometimes, when the collisions occur the asteroids completely fall apart, land on a bigger body participating in this collision. If such “debris” happen to meet another asteroid, part of it gets melted, and another part can bounce back to the space. If we hold such as a meteorite from asteroid belt in our hands, we need to be aware that this is a primitive building material of our Solar System.

Illustrations: A non-zero angular momentum a pre solar nebula created a massive disc in which particles, dust, and derbies was condensed...  •  There is certain unused planet building material in the space between Mars and Jupiter – asteroids  •  Asteroid 243 Ida

Sources: NASA, Internet

See also: Meteoroid

The common iron (2cd)

In the space, the iron can be found as easily as oxygen. Its composition and origin may be different. Based on this, scientists divide iron meteorites into two basic groups. The first account for the meteorites which were parts of a core of huge planetoids, where heavy iron accumulated when the planetoid was very hot and liquefied. Such meteorites contain a very small amount of silicates.
  The second group are the meteorites that derive from the surface of the planetoid which collided with other planetoids. The impact energy caused melting of the bodies participating in the collision and the iron moved down to places located in lower parts of the rocks. In this group of meteorites we will find some inclusions, such as graphite, iron carbide, iron sulphide, iron phosphides and silicates.
  The iron meteorites are quite easy to be found. Among our terrestrial rocks it is not that easy to spot the stony meteorite looking so similar to our rocks. In contrast, solid iron pieces lying on the surface of fields attract our attention immediately. If these pieces are not man made, we there is a big chance we just discovered a new meteorite. This explains the fact why there is quite a high number of meteorites in private collections, even though iron meteorites are very rare in general constituting only 4.5% of total meteorites falls.
  The iron in space is a product of dying stars –meteorites presented here witnessed many cosmic catastrophes in their “lives”.

Illustrations: The distribution of elements in space  •  Iron-nickel core of a differentiated planetoid

Sources: Jeff Kuyken, Jan Woreczko, Internet

See also: Żelazo (iron)

The types of meteorites (2f)

The meteorites are divided into three main groups: stony, iron stony–iron meteorites. Scientists divide them further into subdivisions which depend on composition and the origin. The most popular are the stony meteorites but they are difficult to be recognized among terrestrial rocks. The iron meteorites fall with much lower frequency but they are much easier to be noticed. Pallasites are rare “treasures”. This is a very common division among the collectors as well.
  More recent classification is based on hypotheses how the meteorites were formed, how the object they originated from had evolved and what trace elements they contain.
  The age of the oldest meteorites is estimated to be over 4.5 milliard years. When our solar system had been created, parts of the primitive material were flying in the unlimited and endless space and the fragments which are still falling on the Earth are called a primitive meteorites. Other meteorites can have much more fascinating histories in their lives as they were parts of much bigger objects. The objects subjected to various chemical and physical deformations which changed the mineral characteristics and composition of a given rock. The meteorites coming from such kind of planetoids or planets are known as differentiated meteorites.

Illustrations: Ordinary chondrite  •  Achondrite, eucrite  •  Carbonaceous chondrite  •  Achondrite, shergottite  •  Stony-iron meteorite pallasite  •  Achondrite, lunar meteorite  •  Iron meteorite

Sources: Oscar Monnig Gallery, Mike Farmer, Wikipedia, Jan Woreczko, Internet

See also: Klasyfikacja meteorytów – schemat (meteorites classifications – scheme)

The fall (3d)

It's not easy to be a meteorite. Meteoroid needs to get to an orbit which will cross with the Earth's orbit. Then it travels through the atmosphere in a spectacular way, and loses 90% of its weight. The process is so sharp that in the last phase the stone is torn into many pieces. Eyewitnesses described it in various ways: soldiers compared it to cannonballs, a cook said it was as if “something tore a bag of flour”, a driver thought of a noise a car makes on a paved road. Some people claimed they saw a devil flying on a piece of rock or a red dragon breathing with fire.

  The hardest thing for an eyewitness to assess is where the stone really fell. This is due to lack of any point of reference in the sky. Many people say a fireball flew low to the ground and disappeared 'somewhere' on the horizon. In fact the stone they saw in north-eastern Africa actually fell in Sudan. Therefore, even though eyewitnesses' reports do help a lot they need to be verified carefully.

Illustrations: That is how the defragmentation looks like  •  Example of the meteorite dispersion ellipse

Sources: NASA, Wikipedia, Internet

See also: Elipsa rozrzutu (strewn field, strewnfield, distribution ellipse)

Wadi look for meteorites (4-3-full)

Sources: Jan Woreczko

Do yourself a picture with the meteorite (A3, A3-add)

The largest known meteorite - Hoba (iron meteorite, ataksite)

In 1920, he was found on a farm 8 km to the west of Grootfontein in Namibia, block 3 x 3 x 1 meter. Weight is estimated at 60 tons.
  The huge stone still there is treated as a natural monument and tourist attraction.

Sources: Internet

Touch a meteorite (A4)

Meteorite does not bite

Sources: Thomas Philippe, Jan Woreczko, Internet

See also

Glossary

Meteorite identification  •  How to recognize NOT a meteorite?

Chondrules

Widmanstätten pattern

Fusion crust, fusion rind

Nickel-test

Etching iron meteorites 

Iron in meteorites 

Webside – wiki.meteoritica.pl

Oxford Research Encyclopedias - Wang Kun, Korotev Randy, Meteorites

Sources

Internet

Own collections