What is "thin section"

Thin \Thin\, a. [Compar. Thiner; superl. Thinest.] [OE. thinne, thenne, thunne, AS. [thorn]ynne; akin to D. dun, G. d["u]nn, OHG. dunni, Icel. [thorn]unnr, Sw. tunn, Dan. tynd, Gael. & Ir. tana, W. teneu, L. tenuis, Gr. ? (in comp.) stretched out, ? stretched, stretched out, long, Skr. tanu thin, slender; also to AS. ?enian to extend, G. dehnen, Icel. ?enja, Goth. ?anjan (in comp.), L. tendere to stretch, tenere to hold, Gr. ? to stretch, Skr. tan. [root]51 & 237. Cf. Attenuate, Dance, Tempt, Tenable, Tend to move, Tenous, Thunder, Tone.]

1. Having little thickness or extent from one surface to its opposite; as, a thin plate of metal; thin paper; a thin board; a thin covering.

2. Rare; not dense or thick; -- applied to fluids or soft mixtures; as, thin blood; thin broth; thin air.
   --Shak.

   In the day, when the air is more thin.
   --Bacon.

   Satan, bowing low His gray dissimulation, disappeared, Into thin air diffused.
   --Milton.

3. Not close; not crowded; not filling the space; not having the individuals of which the thing is composed in a close or compact state; hence, not abundant; as, the trees of a forest are thin; the corn or grass is thin.

   Ferrara is very large, but extremely thin of people.
   --Addison.

4. Not full or well grown; wanting in plumpness.

   Seven thin ears . . . blasted with the east wind.
   --Gen. xli. 6.

5. Not stout; slim; slender; lean; gaunt; as, a person becomes thin by disease.

6. Wanting in body or volume; small; feeble; not full.

   Thin, hollow sounds, and lamentable screams.
   --Dryden.

7. Slight; small; slender; flimsy; wanting substance or depth or force; superficial; inadequate; not sufficient for a covering; as, a thin disguise.

   My tale is done, for my wit is but thin.
   --Chaucer.

   Note: Thin is used in the formation of compounds which are mostly self-explaining; as, thin-faced, thin-lipped, thin-peopled, thin-shelled, and the like.

   Thin section. See under Section.

Section \Sec"tion\, n. [L. sectio, fr. secare, sectum, to cut; akin to E. saw a cutting instrument: cf. F. section. See Saw, and cf. Scion, Dissect, Insect, Secant, Segment.]

1. The act of cutting, or separation by cutting; as, the section of bodies.

2. A part separated from something; a division; a portion; a slice. Specifically:

   1. A distinct part or portion of a book or writing; a subdivision of a chapter; the division of a law or other writing; a paragraph; an article; hence, the character [sect], often used to denote such a division.

      It is hardly possible to give a distinct view of his several arguments in distinct sections.
      --Locke.

   2. A distinct part of a country or people, community, class, or the like; a part of a territory separated by geographical lines, or of a people considered as distinct.

      The extreme section of one class consists of bigoted dotards, the extreme section of the other consists of shallow and reckless empirics.
      --Macaulay.

   3. One of the portions, of one square mile each, into which the public lands of the United States are divided; one thirty-sixth part of a township. These sections are subdivided into quarter sections for sale under the homestead and pre["e]mption laws.

3. (Geom.) The figure made up of all the points common to a superficies and a solid which meet, or to two superficies which meet, or to two lines which meet. In the first case the section is a superficies, in the second a line, and in the third a point.

4. (Nat. Hist.) A division of a genus; a group of species separated by some distinction from others of the same genus; -- often indicated by the sign [sect].

5. (Mus.) A part of a musical period, composed of one or more phrases. See Phrase.

6. The description or representation of anything as it would appear if cut through by any intersecting plane; depiction of what is beyond a plane passing through, or supposed to pass through, an object, as a building, a machine, a succession of strata; profile. Note: In mechanical drawing, as in these Illustrations of a cannon, a longitudinal section

   1. usually represents the object as cut through its center lengthwise and vertically; a cross or transverse section

   2. , as cut crosswise and vertically; and a horizontal section

   3. , as cut through its center horizontally. Oblique sections are made at various angles. In architecture, a vertical section is a drawing showing the interior, the thickness of the walls, etc., as if made on a vertical plane passed through a building.

      Angular sections (Math.), a branch of analysis which treats of the relations of sines, tangents, etc., of arcs to the sines, tangents, etc., of their multiples or of their parts. [R.]

      Conic sections. (Geom.) See under Conic.

      Section liner (Drawing), an instrument to aid in drawing a series of equidistant parallel lines, -- used in representing sections.

      Thin section, a section or slice, as of mineral, animal, or vegetable substance, thin enough to be transparent, and used for study under the microscope.

      Syn: Part; portion; division.

      Usage: Section, Part. The English more commonly apply the word section to a part or portion of a body of men; as, a section of the clergy, a small section of the Whigs, etc. In the United States this use is less common, but another use, unknown or but little known in England, is very frequent, as in the phrases ``the eastern section of our country,'' etc., the same sense being also given to the adjective sectional; as, sectional feelings, interests, etc.

In optical mineralogy and petrography, a thin section (or petrographic thin section) is a laboratory preparation of a rock, mineral, soil, pottery, bones, or even metal sample for use with a polarizing petrographic microscope, electron microscope and electron microprobe. A thin sliver of rock is cut from the sample with a diamond saw and ground optically flat. It is then mounted on a glass slide and then ground smooth using progressively finer abrasive grit until the sample is only 30 μm thick. The method involved using the Michel-Lévy interference colour chart. Typically quartz is used as the gauge to determine thickness as it is one of the most abundant minerals.

When placed between two polarizing filters set at right angles to each other, the optical properties of the minerals in the thin section alter the colour and intensity of the light as seen by the viewer. As different minerals have different optical properties, most rock forming minerals can be easily identified. Plagioclase for example can be seen in the photo on the right as a clear mineral with multiple parallel twinning planes. The large blue-green minerals are clinopyroxene with some exsolution of orthopyroxene.

Thin sections are prepared in order to investigate the optical properties of the minerals in the rock. This work is a part of petrology and helps to reveal the origin and evolution of the parent rock.