thinsection

A thin section is a very thin slice of a material, typically about 30 micrometers thick, prepared for examination under a petrographic microscope. It is mounted on a glass slide with a resin or epoxy backing to preserve its structure and to enable precise optical analysis of minerals and textures.

Preparation of a thin section involves selecting a representative portion of a rock or other material, cutting it with a precision saw, and mounting it on a glass slide. The sample is ground and polished through progressively finer abrasives until the desired thickness is achieved, usually around 30 micrometers. The section is then trimmed, finished, and labeled for archival storage. The standard thickness ensures consistent optical properties for microscopy and comparison between samples.

Under transmitted light, thin sections are examined first in plane-polarized light to identify mineral colors and pleochroism, and then in crossed polars to reveal interference colors, birefringence, and crystal habits. Additional techniques may include reflected-light microscopy for opaque minerals, and various immersion methods to determine refractive indices. Petrographic analysis focuses on mineral identification, texture, grain relationships, porosity, and metamorphic or deformation features, providing information about the rock’s history and formation conditions.

Thin sections are widely used in geology, petrology, mineralogy, archaeology, and materials science. They enable non-destructive study of microstructures and mineralogy, support quantitative analyses, and facilitate documentation and comparison across studies. Limitations include potential preparation artifacts and the fixed thickness that may constrain some measurements; standard practices mitigate these issues to ensure consistency and reliability.