How do geologists measure the magnetic direction of minerals in rocks?
152758
The measure magnetic fields with a magnetometer.
1159847
pole\nmagnetic pole, the two nearly opposite ends of the planet where the earth's magnetic intensity is the greatest, as the north and south magnetic poles. For the magnetic north, it is the direction from any point on the earth's surface linking the horizontal component of the magnetic lines of force with the observer and north magnetic pole; it is similar for magnetic south. The north magnetic pole, first located (1831) by English explorer Sir James C. Ross, is now about 78°N and 104°W in the Queen Elizabeth Islands of northern Canada. The south magnetic pole, reached (1909) by English geologists Sir T. W. E. David and Sir Douglas Mawson, is now about 66°S and 139°E on the Adélie Coast of Antarctica. The magnetic poles are not fixed but follow circular paths with diameters of about 100 miles (160 km). Studies of paleomagnetism also indicate that the earth's magnetic field has reversed its polarity many times in the geologic past. The best hypothesis to date for the origin of terrestrial magnetism is the self-exciting dynamo theory, where the earth's magnetic field is generated by the interaction of motion and electrical currents in the earth's liquid outer core.\n\n///\nMagnetic fields are produced by the motion of electrical charges. For example, the magnetic field of a bar magnet results from the motion of negatively charged electrons in the magnet. The origin of the Earth's magnetic field is not completely understood, but is thought to be associated with electrical currents produced by the coupling of convective effects and rotation in the spinning liquid metallic outer core of iron and nickel. This mechanism is termed the dynamo effect. \nRocks that are formed from the molten state contain indicators of the magnetic field at the time of their solidification. The study of such "magnetic fossils" indicates that the Earth's magnetic field reverses itself every million years or so (the north and south magnetic poles switch). This is but one detail of the magnetic field that is not well understood\n\n....\nIn order to explain the fact that ferromagnetic materials with spontaneous magnetisation could exist in the demagnetised state Weiss proposed the concept of magnetic domains. Weiss built on earlier work carried out by Ampère, Weber and Ewing suggesting their existence. The findings of this work revealed that within a domain large numbers of atomic moments are aligned  typically 1012-1018, over a much larger volume than was previously suspected. The magnetisation within the domain is saturated and will always lie in the easy direction of magnetisation when there is no externally applied field. The direction of the domain alignment across a large volume of material is more or less random and hence the magnetisation of a specimen can be zero.\n\nMagnetic domains exist in order to reduce the energy of the system. A uniformly magnetised specimen as shown in figure 5(a) has a large magnetostatic energy associated with it. This is the result of the presence of magnetic free poles at the surface of the specimen generating a demagnetising field, Hd. From the convention adopted for the definition of the magnetic moment for a magnetic dipole the magnetisation within the specimen points from the south pole to the north pole, while the direction of the magnetic field points from north to south. Therefore, the demagnetising field is in opposition to the magnetisation of the specimen. The magnitude of Hd is dependent on the geometry and magnetisation of the specimen. In general if the sample has a high length to diameter ratio (and is magnetised in the long axis) then the demagnetising field and the magnetostatic energy will be low.\n\nThe break up of the magnetisation into two domains as illustrated in figure 5(b) reduces the magnetostatic energy by half. In fact if the magnet breaks down into N domains then the magnetostatic energy is reduced by a factor of 1/N, hence figure 5(c) has a quarter
907372
A magnet whose magnetic properties is dependent on current flow.
699104
Compass needles align themselves with the magnetic field directions. On earth, the magnetic field direction is always from the north pole to the south pole (approximately), hence the compass shows north and south directions.\n\nThus, if in a particular location in space there is a magnetic field, the compass will align itself with it, otherwise, if there is no magnetic field around (most likely in your assumption of space) the needle will not try to show any direction, as you turn the compass, the neddle will freely turn with it.
341358
The north and south poles will be at opposite ends of the object and will lie along the axis of the applied magnetic field that was used to produce the ring or marble magnet.\n\nThe poles in the case of the ring can be produced  on a line (axis) perpendicular to the ring (circle), or it can be produced along a line (axis) that passes through the ring material (the circle). Using the iron filings and multiple orientations will assist you in determining the general direction of the axis of the field, but will not tell you precisely where the poles are.
698855
The directional North pole of the earth is a magnetic south pole, this is because the north end of a compass points north, and opposites attract, therefore north is...south.\n\nMagnetic lines go from south to north i think, sorry havn't taken electricity/mag class in so long...\n\nanyways, if my thining is correct than it would point towards the directional south\n\ni'd choose "down"
582542
Firstly a geophysical survey should be undertaken to allow mapping of the sub surface structures and determine if there is a potential for a accumulation of oil or even gas in a reservoir. I have to admit that im not an expert on gravitational or magnetic data but I work with radioactive and electrical resistivity methods whilst drilling. Best thing to do is email me exactly what your require to know about resistivity and radioactive survey methods and I can whip up some easy examples for you and also explain it to you.
1094906
Above the line, the directon is north\n\nBelow the line, the direction is south.\n\nI think.  From what i remember, you use the right-hand rule.  Imagine pointing your right thumb toward west.  Your four fingers, will indicate the direction of the magnetic field.
1018515
Any two magnetic fields will interact with each other. The same happens with the Earth's magnetic field and a magnet, although the Earths magnetic field density is very weak in comparison to a magnet. \nThe magnet will locally distort the Earths magnetic field, which can be seen by looking at a compass in just the Earth's magnetic field, then looking at the compass when a magnet is brought near.
317463
When liquid magma comes out of the earths crust at the mid-oceanic ridge, it cools rapidly forming crystals. These crystals have magnetic properties that align the crystal according to the earths magnetic field at the time they cooled, similar to how a compass needle points north, the magnetism in the crystal indicates which direction was north when the crystal was formed.\n\nHowever, the direction that is north today, was not always north in the past, in fact many times in geologic history, the north and south poles were reversed entirely. This is reflected in the "magnetic bands" found in rock on the ocean floor.\n\nSo, if you imagine the Atlantic Ocean between the U.S. and Europe, there is a mid-ocean ridge between the two. If the plates never moved, then the magma coming out of this ridge would just pile up, but instead, this is the "engine" that moves the plates away from one another. As you move from the mid-ocean ridge towards the continents, the crystals in the rock have different magnetic orientations that show these flip-flops of the earths magnetic field through geologic history. Because this material originated at the mid ocean ridge, but is now closer to the continents, it shows that the earths crust, the floor of the ocean, is moving AWAY from the mid-ocean ridge and TOWARDS the continents.\n\nThere are a lot of  diagrams that would probably help you understand this better. CHeck out a geology book, or look online.\nGood Luck!
168572
Sea Floor Spreading Evidence- age of land and seamounts are youngest closest to a divergeant boundary.  Magnetic anomalies are the same on both sides of the boundary.\n\nIsopotic Dating- allows geologists to correlate rocks based on radioactive isotopes present.  The ratio of radiogenic daughter isotopes to the unstable parent isotope determin how long the parent has been incorporated in that mineral.\n\nMagnetic Pole Reversals-a thing called remanent magnetism is a component of a rock.  when the rock formed it shows where the earth's magnetic field was at the time.  Measurement of the orientation by inclination angle (latitude) and declination angle (longitute) gives clues to the paleolatitude of the sample when formed.
41444
There are some natural magnets. For example, the mineral magnetite is magnetic, and is found in lodestones. \n\nIf you have a magnet, you can stroke a piece of metal (not all metals, but some) and magnetize it; that is, turn it into a magnet. You line up the magnetic domains when you stroke it so it has a net magnetic field. If you put a radio reciever nearby tuned to the right frequency, you can hear the domains flip as you do this; this is called the Barkhausen effect. \n\nThere are also electromagnets. Passing an electric current through a coiled wire wrapped around the right kind of metal (called a shunt) produces a magnet. This is the kind of magnet one finds in MRI machines.
457011
Distinguishing between the two mineral groups with the microscope can be accomplished quickly by crossing the polars, with the following being obvious:\n\nAll isotropic minerals will appear dark, and stay dark on rotation of the stage. \nAnisotropic minerals will allow some light to pass, and thus will be generally light, unless in specific orientations. \nWhy are isotropic materials dark?\n\nIsotropic minerals do no affect the polarization direction of the light which has passed through lower polarizer; \nLight which passes through the mineral is absorbed by the upper polar. \nWhy do anisotropic minerals not appear dark and stay dark as the stage is rotated?\n\nAnisotropic minerals do affect the polarization of light passing through them, so some component of the light is able to pass through the upper polar. \nAnisotropic minerals will appear dark or extinct every 90° of rotation of the microscope stage. \nAny grains which are extinct will become light again, under crossed polars as the stage is rotated slightly\n\nAnisotropic minerals differ from isotropic minerals because:\n\nthe velocity of light varies depending on direction through the mineral; \nthey show double refraction. \nWhen light enters an anisotropic mineral it is split into two rays of different velocity which vibrate at right angles to each other.\n\nIn anisotropic minerals there are one or two directions, through the mineral, along which light behaves as though the mineral were isotropic. This direction or these directions are referred to as the optic axis.\n\nHexagonal and tetragonal minerals have one optic axis and are optically UNIAXIAL.\n\nOrthorhombic, monoclinic and triclinic minerals have two optic axes and are optically BIAXIAL\nbasically the ones light can travel thruogh are isotropic, like garnets,emeralds,quartz.\nminerals light does not travel through are anisotropic.
89723
Some are moving away from each other (i.e. their separation is increasing), such as Africa and South America. Some are moving closer together, like North America and Asia. Some places continents or pieces of continents are moving past each other, like in the Pacific Northwest, or in the Afar Triangle in Somalia. Some places are expanding, like Iceland. \n\nThere are lots of ways to measure this, but the first clue that something was going on came from looking at the shapes of coastlines. Look at the coastlines of western Africa and eastern South America. They look like they could fit together, like a puzzle. The rocks match each other on both continents too, as if the two continents were once fit together. \n\nHowever, the big clue that something was going on came from magnetic stripes on the sea floor. As new basalt forms in the middle of the Atlantic, and some other oceans, it pushes out from the central mid-ocean ridge, and cools. When it cools, it sets, taking on a magnetization aligned with the magnetic field of the earth at that moment. However, the earth's magnetic field flips every few thousand years (just like the Sun's does, every 11.5 years or so). This creates a record of magnetic stripes on the sea floor that alternate polarity. When the scientists Vine and Mathews saw this, they knew they had proved that plate tectonics existed, and that the continents were moving (sometimes away from each other, and sometimes towards each other or past each other)
511616
First: Gravity is due to mass, while magnetism is due to the movement of an electric charge.  For earth, this is believed to be caused by the movement of ions within the earth, the magma near the core.\n\nSecond: The poles of a magnet were misnamed.  They named the poles of a magnet because of the direction they pointed.  However, once the properties of magnetism were truly understood, it was too late.  So, appropriately, it could be said that near the north pole is the south magnetic pole, but I'm sure most teachers would frown upon that assertion.\n\nOther notes about magnetism on earth: The earth is imperfect.  The magnetic field is not uniform, so there are variations.  Magnetic north is not geographic north in all situations.  The earth is tilted, and we don't really know the flow of the magma that causes the magnetic field all that well.  Not to mention, there is speculation that magnetic north and south may flip at some point in time, but the mechanism of this is lost on me.  It has happened a very long time ago, and is expected to happen again sometime in the future.
474837
The direction of the north magnetic pole on the earth changes slowly over time. In addition, occasionally, the north and south poles reverse with the pole in the northern hemisphere becoming a south magnetic pole and vice versa. This can be recorded in magnetic rocks and even has utility as a dating method. According to our understanding right now, we are in the middle of such a switch. This is why the strength of the magnetic filed is decreasing. Anyway, a shift is when one of these switches happens.
920208
If the current is flowing into the paper from up to down, then using the right-hand rule, we determine that the magnetic field lines are in concentric cirles rotating in a clockwise direction.