Many rocks contain iron-bearing minerals that act as tiny magnets. As magma or lava cool, these minerals begin to form. At this point the molten rock has not completely solidified, so the magnetic minerals floating in the molten mass, become aligned to the magnetic field. Sedimentary rocks also have a magnetic record. Sign In or Create an Account.
User Tools. Sign In. Advanced Search. Skip Nav Destination Book Chapter. Author s. Slichter L. Google Scholar. Get Permissions. Susceptibility and remanent magnetization of rocks View Large.
You do not currently have access to this chapter. You could not be signed in. Librarian Administrator Sign In. First, the team used a strong magnetic field to erase any magnetism naturally trapped in the sample. Then the researchers heated the rock inside a strong magnetic field according to a specific recipe: 25 days at 50 degrees Celsius, then 25 days at 70 degrees, 25 days at 80 degrees, 10 days at degrees, and a final 10 days at degrees. It increased most quickly during the earliest days of each step.
The growing magnetism of the samples suggests that the heat triggered reactions that caused some of the pyrite to chemically transform into magnetic minerals. Analyses conducted after the heating suggest that the magnetic minerals were very tiny grains of magnetite.
These grains were so small, less than 20 nanometers across, that it would take more than 1, of them side by side to stretch across the width of a single human hair. The researchers reported their results online August 10 in the scientific journal Geochemistry, Geophysics, Geosystems.
Stony meteorites contain small flecks of metal that are evenly distributed throughout the meteorite. This is a definitive test of a meteorite, but requires a chemical analysis or acid etching to detect. See more about metal objects below. Unusual density is one of meteorites' more characteristic features. It's not enough to say your rock is heavy. Density is how heavy a rock is for its size or compared with other rocks. Iron meteorites are 3. Lumps or fragments of man-made materials, ore rocks, slag the byproduct of industrial processes and the iron oxides magnetite and hematite, are also common all throughout the world and are frequently dense and metallic.
So this test is helpful but not definitive. To measure the density of your rock, you need to measure its weight and its volume. For the volume, get a household liquid measuring cup that is bigger than your rock and fill it halfway with water. Put the rock in and measure how high the water comes now.
Subtract the first number from the second number to get the rock's volume. Measure the longest side and the shortest side, then one more length perpendicular to both sides.
Calculate a rough volume by multiplying all three lengths together. Most meteorites contain some iron-nickel metal and attract a magnet easily. You can use an ordinary refrigerator magnet to test this property.
A magnet will stick to the meteorite if it contains much metal. Some meteorites, such as stony meteorites, contain only a small amount of metal, but will attract a magnet hanging on a string.
Metal detectors can alert you to whether a rock contains metal, but not all metal is magnetic. For instance, aluminum sets off metal detectors but is not magnetic.
So, if you find a rock with a metal detector, try the magnet test too. In addition to meteorites containing iron, there are man-made and naturally-occurring materials that are magnetic and are easily confused with meteorites. Magnetite and hematite are common iron-bearing minerals that are often mistaken for meteorites.
Both minerals can occur as large masses with smooth surfaces that are heavier than typical rocks, but have some features which resemble meteorites. Magnetite is very magnetic hence its name and hematite is mildly magnetic.
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