Hoba Meteorite: the Largest Iron-nickel Meteorite on Earth
On another Forum a few of us were discussing wedding bands and materials used. I suggested something new that I have seen; his and hers wedding bands and other meteorite jewelry made from meteoric iron-nickel. The inner band is polished and acid-etched to reveal the Widmanstätten pattern and presumably, sealed in some durable clear coating to prevent oxidation (rust.)
This would be a very special token of exchanged marriage vows in the form of enduring space iron that is as old and timeless as space itself. The couple in question will be considering my suggestion. I excused myself from the forum to do my own research of which this composition is the result.
Iron-nickel alloy meteorites have been used by a number of pre-industrial and primitive cultures around the world for the creation of tools and weapons. Native (of Earth) iron on the surface is very rare. Nearly any iron-nickel node found on the surface of Earth that is not embedded in another form or rock, is meteoric in nature. Native iron nodes are known to form on or near the surface of the Earth, but these are naturally-occurring and not meteoric.
Just like deep within the Earth, iron and nickel tend to be found alloyed together which is the basis for the current supportive proof that iron-nickel meteorites originated from the core of a rocky Earth-like planet that was destroyed billions of year ago, or formed from debris of the early solar system that failed to coalesce into a planet in the first place. The asteroid belt between Mars and Jupiter is the main suspect either way. Distinquishing Earth-natural iron and genuine meteoric rocks is difficult until you become familiar with these differences.
The meteoric iron as found on the surface of Earth is heated in a kiln or furnace then either poured or pounded (probably a combination of both) into whatever tool was required. Other tools such as spears and axes could then be forged and used for the acquisition of food such as the capture and slaughter of sea mammals as is the case with the Inuit.
Meteorite-sourced iron-nickel weapons would also be used for defense and aggression against other tribes. Iron provides a distinct advantage over most other available materials for all these human needs. Native iron-tipped tools were actually created using meteoric iron, material that originated from outer space!
(image source) (Widmannstätten texture of an etched meteorite, sample shown from the Gibeon cluster, Namibia)
Widmanstätten patterns are a definitive test for iron-nickel meteorite identification as these patterns do not occur in Earth-created iron alloys. These line pattern are caused by the slow cooling and crystallization within the core of iron-nickel asteroids
Shooting Star? Iron Meteorite Rarity?
Iron-nickel meteorites are over-represented in collections around the world. These only account for less than 6% of the meteorites that actually fall to the Earth but because of their material, are easiest to identify. Also, detection of any ‘iron’ node in the desert by use of a metal detector is virtually without exception, an iron-nickel meteorite. Thousands of stony meteorites may have been overlooked for every iron meteorite found. The fact is that some 90% of all meteorites are ‘stony’ in composition and go undetected. Sometimes however, it is very obvious like when a meteorite strikes your house or office...
Being iron, these rarer iron-nickel meteorites withstand the ablative heat and stresses of entry through the atmosphere and survive the transit to Earth's surface. Stony meteorites tend to explode in the air or completely burn up before striking the ground. A stony meteorite that survives the fall to the Earth erodes like any other rock, turning to sand and dust. Except for oxidizing degradation, Iron meteorites withstand weathering better than do stony meteorites.
Iron meteorites that fall near or in water (especially marine/salt water) tend to rust away quicker in geologic terms.
Iron meteorites tend to be found in greater numbers in the dry desert mainly because of the absence of rainfall and lower humidity. The ones that are found unless they are from very recent meteor falls unless in a very arid desert tend to be like rusticles, caked with rust and having a rich rusty patina. This coloration only increases their attractiveness to meteorite collectors.
Iron meteorites found in the desert get rusty-colored too, but it is far more subtle due to how slowly they have acquired this patina. Often this occurs over the course of hundreds of years or more. It is unusual to discover an iron meteorite near sources of water such as rivers, floodplains and lakes although not impossible or unheard of. These specimens tend to rust completely away in the highly humid or genuinely wet environments (especially near/in salt water) within a hundred years or considerably less.
The largest iron-nickel meteorites ever discovered is the Hoba Meteorite near Grootfontein, Namibia. This meteorite has the distinction of being the largest known whole meteorite and also has the attribute of being the largest naturally-occurring (not man-made) piece of iron on Earth’s surface.
Hoba Iron-Nickel Meteorite as it was Found
The particular meteorite has an unusually high composition of nickel (16%) to iron (84%) ratio, which causes it to fall within the ataxite classification. This is a classification of high nickel-bearing meteorite that does not display Widmanstätten patterning when polished and etched with acid.
The unique composition of ataxite meteorites makes it possible to speculate even from what particular asteroid the meteorite may have originated from. Asteroid impacts shed material on impacts with other space rocks and continue along their orbital path, eventually to a collision with Earth. Analysis of asteroids has revealed distinct compositional differences that can (if fortunate) be shown to have similar properties to Earth-found samples and correlate as their source.
Close-up of Hoba Meteorite
Super Close-up of Vandalism of Hoba Meteorite
In the past this meteorite was subject to vandalism and theft. People would gouge, chisel, break or hack chucks off of it for souvenirs and carry it away. This meteorite is now classified as a national treasure and is monitored and protected under Namibian law.
Identifying a metallic node or object as being meteoric in nature is tricky. There are certain features that things that are consistent and mutually exclusive to identify meteoric versus Earth materials. Iron-nickel meteorites tend to be heavy, heavier than naturally-occurring terrestrial iron nodes. Most people admit surprise when they hold a genuine iron-nickel meteorite for the first time, often commenting how heavy they really are. This is because meteorites as they were formed do not have any air or gas pockets. Many Earth-formed metal nodes do have pockets of gas and voids, which decrease the specific gravity.
Meteorites and Magnets
An iron-nickel meteorite will be only weakly attracted to a magnet; as opposed to man-made metallic objects with have rusted to the extent that identifying the object form becomes questionable. -Is it a meteorite or a highly-rusted prospectors pick or some other man-made tool is a common occurrence.A simple magnet test provides an important clue:
Man-made iron objects are highly attracted to a magnet, even the rusty ones.
There are Earth-native basalts that meet both the criteria of being surprisingly heavy and having no air bubbles present. But if they cut, polished smooth and acid-etched will not reveal the distinctive Widmanstätten pattern.
In my personal collection I have several possible meteorites which have passed every test but the Widmanstätten pattern confirmation (yet to be performed.) I also have found several pieces (over a dozen) of dark metallic-gray nodes which look very much like iron meteorites (as a whole, are heavy, rusted, weakly attracted to a magnet, no bubbles/air pocket visible, etc.) but they have failed in at least one test each and therefore, are definitely not of outer space origin.
They still look pretty fantastic as objet trouvé on my desk. Meteorites are everywhere you go. You just have to know how to identify them.