Polarized light microscopy is used for a wide range of applications in the earth sciences and quality control in various industries:
- Earth Sciences: geology, petrography, mineralogy, crystal structure characterization, asbestos analysis, and coal analysis (vitrinite reflectance)
- Quality control: glass (stress birefringence or inclusions), plastics and polymers (stress birefringence), textiles and fibers, electronic displays, and examination of liquid crystals.
A variety of polarizing microscope images from geological and industrial applications are shown in this gallery.
The term asbestos covers 6 natural silicate minerals with different properties. Each one consists of long, flexible crystal fibers. Asbestos was used as a building material many years ago before it was known to be a health hazard. If found in an old building, depending on the type, costly disposal may be necessary.
Ores are natural rocks that contain valuable minerals. Ores are typically gathered by mining and then further processed so the desired minerals are extracted. Metal ores are often oxides, sulfides, or silicates. The crystal structure and composition of ores can be characterized with polarized light microscopy.
Polarization microscopy quickly provides useful information about fibers, such as human hair or natural (e.g., wool, cotton, silk, etc.) and synthetic (e.g., polymers like polyamide nylon, polyester, rayon, etc.) fibers. Often this information can help distinguish them.
The crystal structure and composition of rocks and minerals can be characterized with polarized light. The examination of rocks with polarized light microscopy normally requires thin sections, approximately 25 µm in thickness, to be produced.
In coal petrography, special oil immersion objectives can be used to differentiate between different coal components (macerals). For these incident light investigations, the coal samples are ground to a high polish. The examination of the coal components allows conclusions to be drawn about the history of the coal deposit, energy content of the coal, etc. The differentiation of macerals is done essentially according to their shape, reflection strength (brightness), and fluorescence characteristics.
An optical technique for observing transparent samples with light that converges into a cone. All directions in which the light propagates can be observed at the same time. Conoscopy is performed with a polarized light microscope using a Bertrand lens. Conoscopy is useful for evaluating the optical properties, for example the number of optical axes, of anisotropic materials.
Residual stress or inhomogeneities in plastics/polymers may occur when they are manufactured. Often, the presence of such stress is unseen and can become a problem that leads to failure. Detection of stress or inhomogeneities with quality control during production can help minimize it. Stressed regions and inhomogeneities present in plastics are visible as bands of multiple colors with polarized light microscopy.
The crystal structure and composition of organic materials can be characterized with polarized light microscopy.