In the realm of geology and geophysics, the term susceptibility (specifically magnetic susceptibility) plays a crucial role in understanding the magnetic properties of rocks. This property essentially measures how easily a rock can be magnetized when exposed to an external magnetic field. It's a fundamental concept used in various geological investigations, from exploring mineral deposits to unraveling Earth's magnetic history.
Susceptibility is defined as the ratio of the intensity of magnetization (I) to the magnetic field (H) projected into the rock. This ratio, denoted by the letter k, essentially quantifies the rock's ability to respond to an external magnetic field.
k = I/H
A higher susceptibility value indicates that the rock is more easily magnetized, meaning it will have a stronger magnetization in the presence of a given magnetic field. Conversely, a lower susceptibility value suggests the rock is less susceptible to magnetization.
Several factors influence a rock's susceptibility, including:
Susceptibility measurements have numerous applications in geological research and exploration:
Various instruments are used to measure susceptibility in rocks, including:
Susceptibility is a key property that allows us to understand the magnetic behavior of rocks and unlock valuable information about Earth's history, mineral resources, and environmental processes. By measuring and analyzing susceptibility, geologists can gain insights into the composition, formation, and magnetic properties of rocks, contributing to a wide range of scientific and practical applications.
Instructions: Choose the best answer for each question.
1. What is magnetic susceptibility?
a) The ability of a rock to resist magnetization.
Incorrect. This describes magnetic permeability, not susceptibility.
Correct! This is the definition of magnetic susceptibility.
Incorrect. This describes the rock's magnetic moment, not susceptibility.
Incorrect. This describes the Curie temperature, not susceptibility.
2. Which of the following factors does NOT influence a rock's susceptibility?
a) Mineral composition
Incorrect. The presence of magnetic minerals greatly affects susceptibility.
Incorrect. Fine-grained minerals generally have higher susceptibility.
Correct! Density itself doesn't directly affect susceptibility, although it might correlate with mineral content.
Incorrect. Susceptibility can change with temperature due to changes in magnetic domain alignment.
3. Which of these minerals is NOT a major contributor to a rock's magnetic susceptibility?
a) Magnetite
Incorrect. Magnetite is highly magnetic and strongly influences susceptibility.
Incorrect. Hematite can be magnetic, although its susceptibility is lower than magnetite.
Correct! Quartz is non-magnetic and does not contribute significantly to rock susceptibility.
Incorrect. Pyrrhotite is a magnetic mineral and influences susceptibility.
4. Magnetic susceptibility measurements can be used for which of the following applications?
a) Mapping underground geological structures.
Correct! Magnetic susceptibility variations can reveal buried features.
Incorrect. While magnetic properties can be used for dating, susceptibility alone might not be sufficient.
Correct! Magnetic minerals often indicate the presence of valuable deposits.
Correct! Paleomagnetic studies use susceptibility measurements of ancient rocks.
5. What is a Kappabridge used for?
a) Measuring the magnetic field strength of a rock.
Incorrect. A Kappabridge measures susceptibility, not field strength.
Incorrect. Age determination requires other methods like radiometric dating.
Correct! This is the primary function of a Kappabridge.
Incorrect. While useful for mapping, a Kappabridge is typically used for point measurements.
Imagine you are a geologist studying a region with potential iron ore deposits. You are using a Kappabridge to measure the magnetic susceptibility of rock samples. You encounter two samples with the following results:
1. Which sample is more likely to contain a higher concentration of iron ore?
2. Explain your reasoning, considering the relationship between magnetic susceptibility and mineral composition.
**1. Sample B is more likely to contain a higher concentration of iron ore.**
**2. Reasoning:** * Iron ore primarily consists of magnetite, a highly magnetic mineral. * A higher magnetic susceptibility value indicates a stronger response to an external magnetic field, suggesting a higher concentration of magnetic minerals. * Therefore, Sample B with its significantly higher susceptibility value is more likely to contain a greater abundance of magnetic minerals, including magnetite, making it a promising indicator for iron ore deposits.