Thin sectioning and mineralogy Sample preparation for rocks, ores, minerals and fossils

Reliable mineralogical analysis starts with sample preparation, not with the microscope. Rocks, ores, minerals, powders and fossils can vary widely in hardness, porosity, structure and sensitivity, making controlled preparation essential for obtaining representative and reproducible results.

From cutting and mounting to vacuum impregnation, grinding, polishing and thin section preparation, each step influences the quality of the final specimen. Incorrect preparation can cause cracks, deformation, material loss, pull-outs and relief formation — and ultimately lead to an analysis that reflects preparation artifacts rather than the material itself.

The following chapters cover the complete preparation chain for geological and mineralogical samples and explain how suitable QATM equipment and QPREP consumables can be selected for different materials, preparation steps and analytical requirements.

Controlled cutting, mounting, grinding and polishing preserve the original structure of rocks, ores, minerals and fossils.

矿物学样品制备 基础与应用

矿物学样品制备通过保留岩石、矿石、矿物、粉末和化石的结构,并为可重复的显微和分析检查做制备,从而为可靠分析奠定基础。

What is thin section preparation in mineralogy?

Thin section preparation is the process of cutting, mounting, bonding to a glass slide, pre-thinning and grinding a rock or mineral sample down to a defined thickness — in most mineralogical workflows approximately 20 to 30 µm — so that the sample becomes transparent and can be examined in transmitted and polarized light.

A thin section is not the same as a polished section. A thin section is examined in transmitted light through both the sample and the glass slide, so thickness and plane parallelism determine whether the optical properties of each mineral phase can be interpreted correctly. A polished section, also called a bulk sample or polished mount, is examined in reflected light, and only the surface has to be flat, scratch-free and free of relief. Thin section preparation adds three steps that polished section preparation does not require: bonding to a glass slide, pre-thinning by cutting, and calibrated final grinding.

矿物学样品制备 矿物样品的切割、镶嵌和浸渍

受控切割、镶嵌和真空浸渍可以稳定矿物样品,保护孔隙和裂缝,并为无损和可重复的进一步制备创造条件。

Which cut-off wheel is suitable for rocks, ores and minerals?

For hard and brittle mineral samples, QPREP diamond precision cut-off wheels are the recommended choice, because diamond as an abrasive cuts the hardest materials and separates them without smearing.

QPREP diamond precision cut-off wheels use a bronze bond. The diamonds can be dressed after longer use, so that the wheel returns to full cutting performance instead of being replaced. Other abrasives are available where the sample allows it.

Cut-off wheel Recommended for
QPREP diamond precision cut-off wheels Hard and brittle mineral samples, rocks, ceramics and specimens with brittle plasma coatings; resin-bonded versions for hard and brittle materials
CBN cut-off wheels Hardened ferrous materials handled alongside mineral samples in the same laboratory
Corundum (aluminum oxide) cut-off wheels Softer ferrous samples and general-purpose sectioning
Silicon carbide cut-off wheels Non-ferrous and mineral materials of lower hardness

Cooling and lubrication matter as much as the wheel itself. An effective coolant supply cools and lubricates the sample during the cut, which reduces thermal damage and dust formation — relevant both for sample integrity and for laboratory hygiene when cutting silicate-bearing rock.

精密切割机 Qcut 200 A

The Qcut 200 A is used in mineralogical laboratories for both cutting and thin section grinding. Functions relevant to geology and mineralogy:

  • several operating modes, including a grinding mode with diamond cup wheels
  • cross feed for larger and irregular samples
  • zone cutting function
  • integrated honing device for diamond cutting discs
  • integrated database of cutting processes
  • high-precision automatic Z-axis for reproducible removal during thin section grinding
The Qcut 200 A covers precision cutting and, in grinding mode with diamond cup wheels, thin section grinding.

Need reliable mineralogy and thin section preparation for your laboratory?

Contact QATM to define the cutting, mounting, impregnation, grinding, polishing and thin sectioning route for your mineral samples. Samples can also be prepared and documented in the QATM application laboratory before a purchase decision.

矿物学样品制备 研磨和薄片制备

研磨、抛光和薄片制备将镶嵌矿物样品转变为具有可靠显微分析所需表面质量和厚度的平整、平面平行的试样。

How are brittle and porous mineral samples mounted?

After mounting, bulk mineral samples and polished sections are prepared according to standard materialographic principles — planar grinding, fine grinding and polishing — for examination in reflected light microscopy and in the scanning electron microscope.

Manual and semi-automatic preparation machines such as the QATM Qpol 300 A1/A2 are used for smaller workloads and for flexible single-sample work. For larger sample volumes, preparation is carried out on fully automatic systems such as the Qpol 250 BOT or the Qpol 300 BOT using central pressure, which keeps parameters identical across a batch.
Surface requirements differ by sample group. Rock samples with high hardness, heterogeneity or texture require a smooth, flat and reflective surface. Ore samples with high density, complex mineralogy or high metal content require a fine, uniform and high-contrast surface so that phases can be distinguished. Mineral samples with high transparency, inherent color or fine texture require a clear, clean and detailed surface.

矿物学样品制备 最终准备、耗材和方法选择

最终制备结果取决于为材料、分析方法和所需的表面或薄片质量选择正确的机器、耗材和制备参数。

When does a thin section need polishing, and which polishing cloth should be used?

Polishing is required when the prepared section is to be examined in reflected light. For examination in transmitted light only, polishing of the thin section is usually not necessary.

The polishing cloth is selected according to the grain size, the abrasive and the polishing objective:

Polishing cloth Suggested grain size Abrasive Properties Application
GALAXY PHI 9 – 1 µm Diamond Medium-hard chemical fiber cloth Pre-, intermediate and final polishing
GALAXY ALPHA 15 – 3 µm Diamond Very hard, perforated chemical fiber cloth Pre-polishing
GALAXY DELTA 9 – 3 µm Diamond Medium-hard silk cloth Pre- and intermediate polishing
GALAXY IOTA 3 – 0.005 µm Diamond, oxide suspension Long-flocked, soft synthetic cloth Final polishing, and fine polishing with fine polishing suspension
Cloth selection follows the required surface quality and the analytical method.

常见问题 - Thin sectioning and mineralogy

What thickness does a mineralogical thin section need?

In many mineralogical workflows the final thickness is approximately 20 to 30 µm. The exact value depends on the material and on the analytical task. Because the sample is bonded to a glass slide, the thickness is assessed optically: correctly thinned quartz appears white, and a yellowish tinge indicates that the sample is still too thick.

Why is sample preparation important in geology and mining?

In geology and mining, sample preparation determines whether the mineral structure is preserved or damaged. Incorrect cutting, mounting or grinding creates cracks, pull-outs, deformation and relief formation, and the analysis then describes preparation artifacts instead of the material.

Which mounting method is suitable for mineralogy and thin sections?

Cold mounting with low-viscosity epoxy resin is the most common method for mineralogical samples and thin sections, because the resin penetrates pores and cracks and because grades with a refractive index close to glass are available. Hot mounting and UV mounting are also suitable, depending on the sample and the preparation goal; UV mounting is the fastest but does not usually achieve complete impregnation of fine pores and cracks.

Why is vacuum needed when impregnating rock samples?

Without vacuum, the air trapped in pores and cracks prevents the mounting material from entering. Evacuating the vacuum container empties the cavities of air, so the low-viscosity mounting material can penetrate them. Filled pores and cracks do not enlarge or break out during grinding and polishing.

How long does epoxy resin need to cure for mineralogical samples?

The curing time of the epoxy resins used for mineralogical samples and thin sections is approximately 3 to 24 hours, depending on the selected material. To reduce bubble formation, samples can be stored for approximately 2 hours at 2 bar overpressure after the mounting mold has been filled.

What is the difference between a thin section and a polished section?

A thin section is thinned to approximately 20 to 30 µm, bonded to a glass slide and examined in transmitted and polarized light. A polished section, also called a bulk sample, keeps its full thickness and is examined in reflected light or in the scanning electron microscope, so only the surface has to be flat and free of relief.

To what thickness is a thin section pre-thinned before final grinding?

After the adhesive has cured, the sample is pre-cut to approximately 300 to 1000 µm while plane parallelism is maintained, using a vacuum clamping device on the Qcut 150 A or Qcut 200 A. The achievable value depends on the material, the mounting and the cutting machine. Final grinding then brings the sample to approximately 20 to 30 µm.

Do thin sections have to be polished?

For many thin sections, polishing is not necessary. Polishing is required when the sample will be examined in reflected light. In that case, GALAXY polishing cloths are selected according to grain size, abrasive and polishing objective.

哪些矿物样品可以使用 QATM 设备进行制备?

QATM equipment is used for rocks, ores, minerals, powders and fossils, including granite, basalt, sandstone, limestone, marble, slate, quartzite, gneiss, iron ore, copper ore, zinc ore, gold-, silver- and platinum-bearing materials, quartz, feldspar, calcite, pyrite, tourmaline, beryl, topaz and fossil material.

Which QATM products are used for thin section preparation?

Qcut precision cut-off machines, QPREP diamond precision cut-off wheels, QATM glass slides, Qpox 90/92/94 adhesives, QPREP 50UV and 55UV light-curing adhesives, the QATM thin section press, vacuum clamping devices, QPREP diamond cup grinders and Qpol grinding and polishing machines.

Can powdered and loose mineral samples be prepared as thin sections?

Yes. Powders and soft rocks must be sufficiently deagglomerated and then fully enclosed by the mounting material, so that particles do not break out later. Low-viscosity epoxy resin is used for thin sections of powdered samples; alternatively, powders can be mounted in a hot mounting press at typical diameters of Ø 25 to 30 mm.

Need reliable mineralogy and thin section preparation for your laboratory?

Contact QATM to define the cutting, mounting, impregnation, grinding, polishing and thin sectioning route for your mineral samples. Samples can also be prepared and documented in the QATM application laboratory before a purchase decision.

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