Iron Woman EarthCache

This EarthCache takes you to the Desert Discovery Center, the permanent retirement home of the Old Woman meteorite; the second largest meteorite ever found in the United States.

The Old Woman meteorite is inside the Desert Discovery Center, which is open 11am to 4pm, Tuesday - Saturday. You must visit during these hours in order to complete this EarthCache.

Meteors are what we commonly call "shooting stars" and are pieces of comets, asteroids or other space debris that enter the earth's atmosphere and burn up in the sky. Meteorites are those same asteroids and pieces material that actually make it all the way to the surface of the earth. Most meteorites that land on the ground are about the size of a grain of sand, each of which make up the approximately 100 tons of particle that bombard the earth daily. Some meteorites have been large enough to leave behind gigantic craters, changing the earth's climate, even causing ice ages. Stony meteorites are the most common while iron meteorites make up only 6% of meteorites landing on earth. However, due to the greater strength, weathering ability and visible difference from the surrounding rock, iron meteorites are much more easily identifiable. Meteorites have been found by humans walking the earth for many many years, often found fashioned into jewelry, tools and even weapons. While stronger than earlier bronze tools and weapons, those weapons and tools fashioned from meteoric iron are more easily broken than iron alloys found or created on earth.

The Old Woman meteorite, discovered: Few meteorites are observed as they fall and no one saw when the Old Woman fell to the ground, but three men did eventually discover the meteor on the desert floor. The Old Woman meteorite originally weighed in at a hefty 6,070 pounds (2,753 kg) when it was discovered in the Old Woman Mountains in the Mojave Desert. The three prospectors were looking for a long lost Spanish mine on BLM land and discovered the big rock in a wash. They were eventually denied their mining claim by the federal government, as meteorites are not considered "locatable minerals" as defined by mining laws and are considered protected by the "Antiquities Act" and an object of national scientific interest. It is unknown how much, if at all, the prospectors were paid by the government for their discovery.

Minerals and Meteorites: There are three basic types of meteorites; stony, stony-iron and iron meteorites. All iron meteorites are derived from the metallic core of their respective parent bodies. That is, they were created in the center of the planet they came from. Iron (Fe) is the most abundant element on the earth but is the 4th most abundant element found on the earth's crust. Pure iron, is actually very soft; softer than aluminum in fact. What makes iron hard are the elemental impurities that are found in the iron as well. For example, a carbon (C) content in iron of .002% to 2.1% makes steel, which is 1000 times harder than pure iron. Iron found on earth typically has little to no nickel (Ni) content, though the earth's core is generally assumed to be an iron-nickel (FeNi) alloy.

Iron meteorites are all of a type of alloy called "meteoric iron," which does not typically exist on earth, except perhaps in the core. Iron-nickel alloys found in octahedrite and hexahedrite type meteorites include kamacite and taenite. An octahedron is an 8 sided shape (shown to the left) and hexahedrons are 6 sided shapes, like a cube. Kamacite contains 5-10% nickel and taenite is 20-65% nickel. Hexahedrites contain only kamacite, with nickel concentrations rarely lower than 5.3-5.8%, and exhibit parallel (Neumann) lines. As the iron alloys cool in octahedrite type meteorites, long nickel-iron crystals of both kamacite and taenite are interwoven to form Widmanstätten or Thompson patterns. (Same thing, two different discoverers). Taenite remains stable at temperatures above 900°C (1,652°F) but between 450°C (842°F) and 700°C (1292°F) kamacite is exsolved (separates) from the taenite. The formation of Widmanstätten patterns occurs when those temperatures are reached and the cooling process occurs at a rate of 100 to 10,000°C/million years over 10 million years. Obviously, these patterns are not reproducible in laboratory settings. These patterns are not typically visible in the surface of meteorites, but are visible in the interior. Sliced pieces, polished and etched with acid make such patterns readily visible.

Both iron and nickel are two of six minerals that are ferromagnetic. Ferromagnetic means they are attracted to magnets and can be magnetized themselves. Ferromagnetic metals include iron, nickel, cobalt (Co), gadolinium (Gd), neodymium (Nd) and samarium (Sm). All other known metals are not ferromagnetic.

Meteorites are classified into 14 categories structurally and by the amount of nickel and trace elements found in the iron. Type IIAB meteorites having the lowest concentration of nickel of all the iron meteorite groups (5.3 to 6.6% Ni)

The Old Woman meteorite, analyzed: The Old Woman was eventually taken to the Smithsonian Institute for analysis. A 942 pound (427 kg) piece of the meteorite was removed from the "bottom" of the rock and analyzed under the supervision of Dr. Roy Clarke. It was determined that the Old Woman was a one of a kind, very unique specimen. It's structure is a transitional variation of two well known types of metallic meteorites, which had never been seen together before. The Old Woman is classified as a type IIAB coarsest octahedrite meteorite, with a nickel content of 6%. The Old Woman also contains small amounts of cobalt, phosphorus (Ph), chromium (Cr), and sulphur (S).

The Old Woman is believed to have formed in the Asteroid Belt in the early stages of our solar system. While a woman will never willingly tell you how old she is, it is believed that the Old Woman meteorite is more than 4.5 billion years old!

When logging a find on this EarthCache:

Include what the meteorite felt like to you in your online log.

Photos are always welcome as long as they do not give away any answers.

Please send the following information via email within two weeks of your "found it" log:

1. Iron Woman EarthCache GC5B0BD
2. The number of people in your group, including yourself =
3. What is are the length and width measurements of the smaller, visibly cut section near the top that was also removed for analysis? (not the bottom she is sitting on)
4. Take a very close look at that flat, cut portion (a magnifying glass may help with this). Other than a polished surface from being touched, describe what you see and explain why that may be. (Can you see the Widmanstätten patterns?)
5. How much does the Old Woman weigh today?
6. Is the Old Woman attractive? Compare how well a magnet adheres to the meteorite and two other common metal items; an ammo can and a nickel (5 cent piece). Give an explanation for why these items are or are not attractive to magnets or each other. Describe any differences you find between their attractiveness. (There's an ammo can nearby) Use a standard ceramic/ferrite (AlNiCo) type magnet and a strong neodymium magnet (NdFeB) for this.

Please do not throw or toss magnets at the meteorite; you do not want to break the nearby window. Logs may be deleted if answers are not received within a reasonable amount of time following your post of a find. The answers are not difficult and may be answered simply by visiting the Old Woman and reading the description.

This EarthCache was created with the permission and support of the Desert Discovery Center

References:

1. http://en.wikipedia.org/wiki/Iron
2. http://en.wikipedia.org/wiki/IIAB_meteorites
3. Desert Discovery Center
4. US Dept of the Interior, BLM information brochure
5. http://www.mnh.si.edu/onehundredyears/profiles/Roy_Clarke.html
6. http://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html#.U_Vy8GPASKs
7. http://en.wikipedia.org/wiki/Widmanstätten_pattern#Lamell.C3.A6_formation_mechanism