Meteorites

 Meteorites in rough shape (we have tons of it!)

 

 




A. Meteorites as Semi-Precious Gemstones

Octahedrite & Pallasite used in Jewelry

Source: Worldwide

A meteorite is an extraterrestrial body that survives its impact with the Earth's surface without being destroyed. While in space it is called a meteoroid. Most meteoroids disintegrate when entering the Earth's atmosphere, however an estimated 500 meteorites ranging in size from marbles to basketballs or larger do reach the surface each year. About 5 percent of meteorites that fall are iron meteorites with intergrowths of iron-nickel alloys, such as kamacite and taenite. Most iron meteorites are thought to come from the core of a number of asteroids that were once molten.
 
About 86 percent of the meteorites that fall on Earth are chondrites or achondrites, neither of which produce a suitable material for jewelry. Chondrites are meteorites of the "stony" type, that have not been modified due to melting or differentiation of the parent body. Chondrules, are composed mostly of silicate minerals that appear to have been melted while they were free-floating objects in space.

Meteorite (octahedrite) pendant by Michael Zobel

Pallasite with transparent olivine crystals

Achondrites are stony meteorites that consists of material similar to terrestrial basalts or plutonic rocks. Only 6 percent of meteorides are "iron meteorites" (octahedrite) or a blend of rock and metal called pallasite.

Octahedrite

The most common class of iron meteorites is octahedrite, which is composed primarily of nickel-iron alloys such as taenite (high nickel content), and kamacite (low nickel content). The nickel-iron alloys in octahedrite have crystallized into intermixed, millimeter-sized bands. When polished and acid etched, these bands show the classic "Widmanstätten patterns" (aka "Thomson structures") of intersecting straight lines (above, left) of lamellar kamacite.

Pallasite

Meteorite that contain fragments of gemmy olivine and/or peridot crystal (above, right) are called pallasite, or "stony-iron meteorite." When sliced into thin layers, these olivine and peridot fragments are transparent next to the opaque nickel-iron matrix they are contained in. Any polished nickel-iron surfaces must be treated to prevent rust and corrosion.
Pallasite is thought to be "impact-generated," forming a mixture of core and mantle materials with the molten iron meteorite. Pallasite is a rare variety of meteorite which has been found in Argentina, Australia, Chile, China, Russia and the United States.

Meteorite (Pallasite) Chemistry & Physical Properties

Name, Atomic Symbol, #	nickel, Ni, 28 / iron, Fe, 26
Element Category	transition metals
Crystal System	body-centered cubic (iron Fe)
Crystal Habit	intermixed, millimeter-sized bands
Specific Gravity (SG)	8.67 (nickel) 7.21 (iron)
Mohs Hardness Scale	6.0 to 7.0
Toughness	excellent (octahedrite) to fair/poor (pallasite)
Chemical Composition	SixOy
Chemical Composition	(Mg, Fe)2SiO4 (Olivine)

Meteorite Optical Properties

Refractive Index	1.540
Surface Luster	vitreous to dull
Diaphaneity	transparent/opaque (pallasite) to opaque (octahedrite)
Gem Color	grey, brownish-grey, black (olivine: amber, greenish-yellow)

Source:  http://www.allaboutgemstones.com/semi-precious_gems_meteorite.html




B. Meteorites Myth

Meteorite Myths

These Meteorite Myths come from an article published by Space.com called The Top 5 Cosmic Myths. Some very interesting reading is presented below.

Myth 1: Meteors are heated by friction as they pass through the atmosphere.

This one makes sense, which is why it's so pernicious. But it's still wrong.

Meteoroids are tiny bits of dust, rock, ice or metal that have the unfortunate luck of having their orbits intersect the Earth's. When they pass through our atmosphere, they are heated so ferociously that they glow (and at this point are called meteors), and are visible for hundreds of miles.

However, it is not friction that heats them. Think of it this way: a space shuttle's tiles are extremely delicate; they crumble easily in your hand. If they were heated by friction as the shuttle de-orbits and enters the atmosphere at Mach 25, the tiles would disintegrate. That's not a very good design characteristic.

In reality, it isn't friction, but ram pressure that heats the meteoroid. When a gas is compressed it gets hot, like when a bicycle pump is vigorously used to inflate a tire. A meteoroid, moving at 33,500 mph (15 kilometers a second) or more compresses the air in front of it violently. The air itself gets very hot, which is what heats the meteoroid. That's the fact, not friction.

Myth 2: Meteors are still very hot when they hit the ground.

You'd expect that something heated up so much that it glows would still be hot a couple of minutes later. Actually, the situation is a bit more complicated.

The super-hot air in front of the meteoroid is not actually in contact with the particle. (A particle can still be referred to as a meteoroid as it races through the atmosphere, while "meteor" is meant to describe the whole glowing phenomenon.)

The meteoroid's quick motion sets up a shock wave in the air, like from a supersonic airplane. The shocked air sits in front of the meteoroid, a few centimeters away (depending on the meteoroid's size) in what's called a standoff shock. Between the shocked air and the surface of the meteoroid is a relatively slow-moving pocket of air.

The surface of the meteoroid melts from the heat of the compressed gas in front of it, and the air flowing over it blows off the melted portion in a process called ablation. The meteoroid's high velocity provides the energy for all this heat and light, which rob it of speed. When it falls below the speed of sound, the shock wave vanishes, the heating and ablation stop, and the meteoroid then falls rather slowly, perhaps at a couple of hundred mph (or a few hundred kilometers per hour).

It's still pretty high up in the atmosphere at this point, and takes several minutes to fall to the ground. Remember, this tiny bit of rock spent a long time in space, and the core is pretty cold. Also, the hottest parts were melted and blown off. Even more, the air up there is cold, which chills the rock as well.

All of these things together mean that not only is the rock not hot when it hits the ground, it can actually be very cold. Some meteorites (what a meteoroid is called after it impacts) have actually been found covered in frost!

C. Fun facts on Meteorites

Meteorite Myths

 

Myth - Meteorites can be highly radioactive.

Truth - Actually meteorites are no more likely to be radioactive than ordinary terrestrial rocks.

 

Myth - Meteorites contain rare elements and exotic materials, like Kryptonite.

Truth - Scientists report that till date, no meteorite has been found to contain any element that does not occur naturally on earth.

 

Myth - Meteorites are rare and account for a very small amount of material reaching the earth.

Truth - Earth accumulates approximately 100 tons of extraterrestrial material every year. The current rate of fall for meteorites, greater than 100g, is approximately 27 per year. Meteorites, as large as a basketball, strike earth approximately once a month, with nearly 75% of the impacts landing in water.

 

Myth - Meteorites are meaningless, except as threats to our existence.

Truth - Besides the known effect they have had on life and dinosaurs, meteorites have revealed or contributed a tremendous volume of natural resources to our planet, through impact.

 

Myth - Meteorites are believed to carry diseases from space, which can harm anyone who comes into contact with them.

Truth - Meteorites do not carry diseases from space. There has never been a sign of any living bacteria or virus associated with, or naturally occurring within, a meteorite. Such germs, as well as spores molds and fungus, may attach to a meteorite after it lands, but that is part of the terrestrialization process. 

 

Myth - When they land on the Earth, meteorites always glow with heat from their passage through earth's atmosphere.
Truth - This is not true. Although there is some controversy as to whether or not some meteorites are warm to touch when they fall, most of them are cool when they land on the Earth's surface. They travel so fast through earth's atmosphere that the heat produced during entry is ablated away, much the same way that the tiles on the underside of the space shuttle (and heat shields on prior space capsules) protect the shuttle. In fact, the aerodynamic shape of oriented meteorites was the inspiration for the blunt heat shield design of the Mercury/Gemini/Apollo space capsules.