Thin section

A thin section is a solid preparation for microscopic examination. Mostly it is rock, ceramics and castings.

Rocks, soils and ceramics are almost always opaque and therefore can not be studied easily under a light microscope. Only at a thickness of 0.03 to 0.02 mm (30 to 20 microns ) can pass sufficient light, a sample of these materials, making them suitable for transmitted light microscopy. Is examined in normal and polarized light as well as with specific wavelengths (e.g., UV light).

• 3.1 overall objectives
• 3.2 qualitative targets
• 3.3 quantitative targets

History

The first experiments with thin sections date back to the English naturalist Henry Clifton Sorby. This published this method for the first time in 1858, through an article in the Journal of the Geological Society in London. Thereafter, this method of investigation moved quickly into the practice of petroglyphs.

On the paleontological research field geoscientists Franz Unger and Carl Ferdinand Peters have acquired early achievements with the thin section microscopy. Unger 1842 described his method of handling of thin sections in the study of fossil woods. By 1840 he had made on behalf of Stephan Ladislaus finite thin sections of such objects. Peters led around 1855 (published ) from thin section work, to gain further insight for taxonomic reviews. At the early spread of this investigation method in geosciences Ferdinand wore circle at crucial that she introduced on February 3, 1863 in a meeting of the Imperial Geological Reichsanstalt and had previously learned at Sorby.

The preparation of thin section images was in the 19th century for the literature only unsatisfactory solvable problem, because the former printing techniques an authentic reproduction of the often demanding structural images not allowed. Therefore, it was sometimes customary to create corresponding thin section images on the drawing paths with subsequent hand-coloring and printing technology implemented by the means of lithography.

Production

Geological and technical preparations

For the manufacture of a stone or a ceramic thin section approximately 0.5-1.0 cm thick slice is sawn from the sample by means of a diamond impregnated saw blade. The disc is on one of the cut surfaces sanded by hand and fixed by a relatively readily soluble adhesive to a thin glass plate with this surface. The glass plate with the sample is then clamped in a precision grinding machine and as long as the sample is ground from the other side until it is completely flat. After the glass plate was removed from the sample with the grinding table, the planar surface is glued by means of a particular synthetic resin to a glass slide. The now almost finished preparation is peeled off after curing of the resin of the glass sheet. The slide is clamped in the precision grinding machine and the sample is now of the other, formerly attached to the glass plate side to the desired thickness ( standard thickness for mineralogical thin sections is 25 microns ) ground down.

Technical preparations grains or unstable sedimentary rocks (eg many quartz sandstone types ) are first cast in resin or impregnated with synthetic resin and after curing of the resin, such as the aforementioned solids processed.

Ground preparations

To produce a soil thin section an undisturbed soil sample by Kubiena kits are (named after WL Kubiena, who has done his work already undertaken since the 1930s, micromorphological studies on soils undoubtedly pioneering work in this field ), and variations of these boxes are used in the field. Is not possible removal with Kubiena Boxes due to high stone contents or larger artifacts, including larger frame can be used or the sample are coated with plaster. In the laboratory soil samples finally dried ( air drying, freeze drying, or drying over acetone) are. They are then in a vacuum oven ( so that no air bubbles remain in the samples ), similar technical grained samples or sediment samples, embedded in synthetic resin. After curing of the resin method as described above is.

For some specific studies ( Microprobe etc. ) uncovered samples are necessary. The sample can, however, also be covered with a cover glass. For investigations eg on the microprobe polished uncovered cuts are necessary, to special methods are needed that do not produce relief.

• Conventional transmitted light microscopy vs. polarization microscopy

Same image cutout as in the picture with crossed polarizers

Rock studies using thin sections

In the investigation of rock samples is distinguished by qualitative and quantitative targets. Furthermore, the general characteristics are the purpose of viewing.

General objectives

• Spatial orientation of crystals and grain aggregates
• Character distribution of minerals in the rock
• Grain or crystal forms
• Grain bonds

Qualitative targets

• Determination of rock-forming minerals
• Composition of mixed crystals by means of optical data
• Degradation processes and their achieved status in crystalline microstructures ( weathering )

Quantitative targets

• Proportions of various minerals in the rock
• Grain size distribution

Results and Interpretation in soil science

Before one can interpret a thin section, it is first necessary (if any) to describe in detail these and other thin section thin sections of other samples that are directly or indirectly in context.

In soil science and archeology are recognized to include:

• The microstructure (aggregates, voids, courses),
• The so-called matrix ( that is, the organic and mineral fine and extremely fine )
• Not embedded in the matrix of organic material and
• The individual soil characteristics and particularities.

To characterize these constituents are each among other things, the size, shape, texture, variability, frequency, color, transparency, value and location of the components to each other and possibly resulting pattern described.

The soil in thin section visible, more or less pronounced features and feature combinations are a "snapshot ": they reflect the development of a soil and the processes in it to resist sampling. From an archaeological point of view, charcoal remains, bone fragments, particles fired clay, slag and Erzreste, excreta, egg shells, fish bones, etc., of particular interest, because - depending on the location in profile - you can ideally based on the " microscopic findings " in thin section ( in conjunction with other thin sections of the same findings as well as any existing " macroscopic artefacts " ) the story of a finding reconstruct: from the former use or function of an object itself ( for example, from pit houses ), over the ambient conditions (eg livestock ) to for backfilling of an object as well as the origin and composition of this backfill material that can document the human activities in the vicinity of the lesion.

Related methods

If opaque materials are examined only in reflected light, satisfy one side ground and polished surfaces on the object, so-called polished sections.

Even within the metallography to work occasionally with microstructure micrographs.

The in medicine this mutatis mutandis related methods are described below and histology microtome.