Principle of Cathodoluminescence Identification of Rocks and Minerals

1. Sample Preparation

First, the cathodoluminescence thin section of rock was made. Compared with ordinary rock thin section, this kind of thin sectionwas not covered, the top surface was polished, and the thickness was slightly larger (0.04mm). It is pasted on the carrier with 502 glue. If there is oil, it should be cleaned first.

2. Principle of Cathodoluminescence

When an electron beam (e.g. from a scanning electron microscope) interacts with minerals, a variety of processes occur, which can be used for various microscopic observations. In addition to electronic signals, various incoherent and coherent processes generate a wide range of electromagnetic radiation.

Cathodoluminescence is most commonly performed in scanning electron microscopy.The vacuum chamber containing the sample you  study, the electron beam is focused on the sample.

Then, the light generated by the sample under the action of electron beam must be collected by collecting optical devices (such as mirrors or objective lens), or captured directly by the cathodoluminescence detector in the chamber. When the light is collected through an optical element, it will be directed to an optical detection element, such as a photomultiplier tube (PMT), spectrometer or camera.

Cathodoluminescence can be used to explore many basic properties of matter. It can be used to study light transmission, scattering, electronic structure of materials, resonance phenomenon and so on. Therefore, it provides a valuable source of information for basic research and applied research directly related to the industry.

Cathodoluminescence is highly related to the field of nanophotonics. It is suitable for metal as well as dielectric and semiconductor nanostructures, including nanoparticles, nanowires, supramolecules, supersurfaces and photonic crystals. These structures can be used in (biological) sensing, fluorescence enhancement, nonlinear optics, low threshold steam generation, led, solar cell, integrated photonics, laser and other fields.

Cathodoluminescence is an ideal tool for studying geological samples and obtaining additional contrast and spectral information at the resolution of SEM.Cathodoluminescence from rocks can provide insight into crystal growth, banding, cementation, displacement, deformation, provenance, trace elements and defect structure.This can be used to fingerprint rocks and display interesting spatial textures in submicron scale.Cathodoluminescence is often used in combination with other analytical tools such as Sims, LA-ICP-MS, BSE, EDS, WDS and μ CT to gain a more comprehensive understanding of all relevant rock properties.

Ceramics, dielectrics and (compound) semiconductors play an important role in many devices and functional materials, including scintillators, phosphors, high-power electronic light-emitting diodes, diode lasers and solar cells. Nanostructures are increasingly used to optimize the optical properties of these materials. Cathodoluminescence can be used to study these materials (bulk and nanostructured materials) and determine their luminescent properties at the nanoscale.

3. Cathodoluminescence Applications in Other Fields

Cathodoluminescence is also increasingly used in soft materials, including polymers and biological tissues.

4. The Principle of Cathodoluminescence Used in the Identification of Rocks and Minerals:

different minerals have different electronic structures, different valence states, different properties and quantities of ligands, and different forms of ligands, which have different effects on their electronic energy levels. Under the electron impact, different minerals emit different light (different colors and intensities).

At present, the cathodoluminescence detection of rock thin section has important application value in the field of sedimentary rock (clastic rock and carbonate rock), and also has certain value in the study of the genesis of magmatic rock and metamorphic rock.

5. Equipment

6. Identification Content

6.1 clasolites

6.1.1 Judging the mineral composition and pore origin of clastic rocks according to the mineral luminescence color

6.1.2 Mineral composition difference: emphasis should be placed on identifying the mineral composition that is difficult to distinguish under the polarized light microscope. The method is as follows:

a) Fe2+/Mn2+ ratio  Determine the luminescent color of carbonate minerals with Fe2+/Mn2+ ratio.

b) Determine the cathodoluminescence color of each mineral in the clastic rock sample.

c) Describe the cathodoluminescence colors of various minerals in clastic rock samples.

d) Determine the origin of quartz.

6.1.4 Distinguish pore origin

The origin of pores should be identified according to the luminescence and observation under polarized light microscope, and the pores should be divided into primary pores and secondary pores. The pore types should be described according to the method given by SY/T 5368.

6.1.5 The cementation mode is identified according to the following methods:

a) Secondary augmentation cementation: the cementation grows around the clastic particles, and the color of luminescence is different from that of the clastic particles, May have a zonal structure.

b) Multi-stage filling cementation: refers to the same type of cementation formed in two or more stages.

c) Fracture cementation: It refers to the fracture formed by the fracture of rock or mineral particles is healed as a whole by the cementation.

d) pressure dissolved chimeric cementation: the particles are in concave-convex or suture line contact, and the content of cement is very little.


Cementation stage, point out two or more than two filling structures of same cement.

6.1.7 Quartz enlargement grade is divided into:

a) Weak: the number of quartz grains with enlargement phenomenon are less than 10% of the the number of quartz grains in the rock.

b) Medium: the number of quartz  grains with enlargement phenomenon accounts for ≥ 10%~ ≤ 50% of the quartz  grains  in the rock.

c) Strong: the number of quartz grains with enlargement phenomenon is greater than 50% of the quartz grains in the rock.

6.1.8 Determine the name of the residual minerals or components that have been dissolved in the rock

6.1.9 Determine the name of the metasomatism and the metasomatized minerals or the metasomatism relationship between them.

6.1.10 Determine the luminescence characteristics of bioclasts and their metasomatism, metasomatism, recrystallization and other characteristics.

6.1.11 Describe the zonal form, zonal number, defects, dissolution, and luminous color of the mineral

6.1.12 Describe the original structures and structures that have disappeared under polarized light microscopy.

6.1.13 According to the luminescent color, sequence and cementation characteristics of authigenic minerals, the diagenetic evolution sequence is determined as shown in Table 4.

6.1.14 According to the number of cracks, width, dissolution and filling composition and filling methods and other characteristics.

6.1.15 Restore the characteristics of the original pores and judge the development characteristics and evolutionary history of the pores

6.1.16 The staining method given by SY/T 5368 is used to distinguish carbonate minerals.

6.1.17 Representative cathodoluminescence phenomena in rock samples should be photographed and well documented.

6.2 Carbonate rocks:

6.2.1 Identify the components, genesis, pore evolution, structure and structure of carbonate rocks.

6.2.2 Emphasis should be placed on the identification of components that are difficult to determine under polarized light microscopy. Including grains (particles), terrigenous minerals, authigenic minerals and interstitial materials:

A) Fe2+ / Mn2+ ratio and luminescent color of carbonate minerals.

B) The relationship between mineral luminescence color and trace elements

C) Cathodic luminescence colors of various components

6.2.3 Distinguish the origin of various pores in carbonate under cathodoluminescence, and divide the pores into primary pores and secondary pores. The pore type description shall be described according to the method given in SY/T5368.

6.2.4 Determine the generation relationship of cements and describe the luminescence characteristics of each generation.

6.2.5 Determine the formation stages of cements and the mineral names of each stage

6.2.6 Describe the location of dissolution pores and the names of dissolved components

6.2.7 Explain the relationship

6.2.8 Bioclasts

6.2.9 Band characteristics

6.2.10 Petrogenic characteristics and diagenetic stages

6.2.11 Describe particles, bioclasts, pores, minerals, structures and structures that have partially or completely disappeared under a polarizing microscope. The lithology of a rock can be inferred by restoring its original structure.

6.2.12 Fracture characteristics

6.2.13 Pore evolution

6.2.14 Distinguish carbonate minerals by staining

6.2.15 Requirements for recording representative luminescence phenomena

6.2.16 Observation Result Description

6.3 Pyroclastic rocks:

6.3.1 Identify the luminescent colors of major minerals, minor minerals and other minerals of pyroclastic rocks. For the identification results, refer to Table A.

6.3.2 Describe the luminescent color of each mineral according to Table 2, and determine the mineral composition which is difficult to identify under polarized light microscope.

6.3.3 Structural restoration,

6.3.4 Describe the alteration of rock samples and indicate the relationship between metasomatism and to be metasomatism

6.3.5 Requirements for recording representative luminescence phenomena

6.3.6  Observation Result Description

6.4 Magmatic rocks

6.4.1 Identify the mineral composition and physical properties of magmatic rocks according to the corresponding observation of cathodoluminescence and polarization, and refer to A.3 for the identification results

6.4.2 Determine mineral composition according to luminous color

6.4.3 Describe the number, period, size, fillings and filling characteristics of pores, holes and fractures in rock samples

6.4.4 Restoration of original structure and structure

6.4.5 Secondary changes and alteration

6.4.6 Record of representative luminescence phenomenon

6.4.7 Description of Observations

6.5 Metamorphic rock

6.5.1 Identify the composition, structure and other contents of the main minerals, minor minerals and other minerals in the metamorphic rocks. Refer to Table A.3 for the identification results.

6.5.2 Determine mineral composition according to luminous color

6.5.3 Restoration of original structure and structure

6.5.4 Secondary changes and alteration

6.5.5 Record of representative luminescence phenomenon

6.5.6 Observation Result Description