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: Meteorite



Octahedrite & Pallasite used in Jewelry


Meteorite


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 Pendant

Meteorite (octahedrite) pendant by Michael Zobel

   Gemmy Meteorite with Olivine

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 "WidmanstŠtten 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)







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