Shlif (from it. Schliff - polished, polished; it. Dünnschliff - transparent shlif) - a thin plate of rock or mineral glued to glass. Standard petrographic section has a thickness of 0.03-0.02 mm, glued on a special resin - Canadian balsam and is covered on top with a thin cover glass. The size of a standard section is approximately 2 × 4 cm. The sections are made primarily for studying rock on a petrographic microscope . The study of thin sections is the main method of the science of petrography .
Content
Standard grinding
The thickness of the standard section is the thickness at which the quartz in crossed nicols has gray colors of interference coloration . In such sections, the optical properties of minerals are relatively constant and standard. In thicker thin sections, many important rock-forming minerals may be opaque (in particular, magmatic amphiboles and pyroxenes ), making it difficult to define them and study relationships. Thinner than standard sections are often difficult to make, and the minerals in them will be colorless, which will also complicate their study.
Canadian balsam as a glue has many advantages. Firstly, its optical properties are constant, and their comparison with the properties of minerals (determination of the mineral group by relief, etc.) is one of the important features. Secondly, the balm melts at a relatively low temperature and is easily dissolved in alcohol, so the thin section on the Canadian balm is easy to remove from the glass.
The big disadvantage of the thin section on the Canadian balsam is that when analyzing on a microprobe, the resin can evaporate under the action of an electron beam and distort the results of the analyzes. Therefore, thin sections glued to epoxy resins are used for microprobe analyzes. In addition, when struck or over time, the balsam may crystallize and the study of such thin sections will become problematic.
Also made the so-called uncoated thin sections without cover glass, which allows you to study them in reflected light and analyze different methods.
Unusual thin sections
Non-standard thin sections are often made, the manufacturing technology of which depends on the objectives of the study.
Thicknesses that are thicker than standard ones are often used to study inclusions in minerals. Both sides are polished on such plates, or a thinner section is made thicker than the standard one, in which the most interesting areas are selected under a microscope and they are peeled off and studied by methods of thermobarogeochemistry , microprobe , etc.
Special methods are used for the manufacture of thin sections that contain water- soluble minerals or melt at room temperature (for example, thin sections of ice or salt ).
Another kind of difficulty is associated with the manufacture of thin sections of rocks containing particularly hard minerals , such as diamonds . In this case, special gentle grinding techniques are used.
When studying the orientation of minerals for microstructural studies of rocks, oriented sections are made. To create oriented sections, it is necessary that the sample itself, from which it is made, be taken with the orientation indicated on it, and this orientation has not been lost during further operations.
Making thin coal is also not a trivial exercise. In order that coal began to appear through, it is necessary to make a thin section with a thickness of 0.01 mm (10 microns). At the same time, coal is fragile, easily deformed and sensitive to heat.
In biology, the thin section method is used for microscopy of strongly sclerified or mineralized objects that cannot be cut on a microtome [1] , as well as in paleontology .
The manufacture of thin sections
The method of producing thin sections depends on the purpose for which they are made. Standard thin sections are massively manufactured in special laboratories. Now special equipment is used for this, which allows to automate the process to a large extent.
The manufacture of thin sections consists of the following basic operations:
- sample preparation: making a suitable size plate from it.
- grinding one side of the sample to which the glass will be glued. Usually it is ground on a not very fine powder, since the weak roughness is smoothed out by the balm and does not interfere with the study.
- glass preparation. The glass must be completely flat, the side on which the thin layer will be glued must be ground on a coarse powder to give it a matte sheen. This is necessary so that the thinning does not peel off.
- gluing the sample to the glass. It is important to avoid trapping air bubbles.
- polishing the sample to a thickness close to the standard.
- fine-tuning the section to standard and uniform thickness over the entire area. The thickness of the thin section is controlled by a petrographic microscope. This is the most time-consuming work, requiring experience and a light hand.
See also
- Anshiff
- Petrography
- Petrology
Notes
- ↑ Barykina R.P. et al. Handbook of botanical microtechnology. Basics and methods. - M .: Publishing House of Moscow State University, 2004 - p. 73-74. ISBN 5-211-06103-9
Links
- Article "Shlif" on wiki.web.ru
- Great Soviet Encyclopedia : [30 tons] / ch. ed. A. M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
- Modern technology for the manufacture of thin sections.