The Subgrain Size Piezometric is done by a Triassic halite from the upper bunter formation in Hengelo, Netherlands. The rock salt halite is white and normally in thin sections are no crystal boundaries observable, because of the cubic crystal structure and its optical isotropy. To make even the sub grain boundaries visible, the sample has to prepared in a special way, where the crystals appear blue and the boundaries white.
For the Subgrain Size Piezometric we uploaded first a picture 430.9-1, which we took as an example, in the program “ImageJ” and changed the type to 8-bit. The next step is adjusting the threshold. The program allows an automatically threshold, but for a better analysis it does be done manually. Figure 1 shows the converted image. Other programs for example MATLAB or ArcGIS can be used as well. [...]
Table of Contents
I. Description of the used method
II. Calculation Results of all Pictures
III. Error calculation
IV. Palaeo-stress
V. References
Objectives and Topics
This study aims to determine the palaeo-stress of halite samples by measuring subgrain sizes using digital image processing techniques. The research investigates whether subgrain boundaries, which are difficult to observe in thin sections due to the mineral's optical isotropy, can be reliably quantified to infer past stress conditions in Triassic rock salt.
- Application of image processing software (ImageJ) for microstructural analysis.
- Methodology for enhancing and thresholding microscopic images of halite.
- Statistical treatment of grain size measurement data.
- Evaluation of error sources such as gas bubbles and crystal fractures.
- Comparison of calculated subgrain sizes with established palaeo-stress models.
Excerpt from the Book
I. Description of the used method
The Subgrain Size Piezometric is done by a Triassic halite from the upper bunter formation in Hengelo, Netherlands. The rock salt halite is white and normally in thin sections are no crystal boundaries observable, because of the cubic crystal structure and its optical isotropy. To make even the sub grain boundaries visible, the sample has to prepared in a special way, where the crystals appear blue and the boundaries white.
For the Subgrain Size Piezometric we uploaded first a picture 430.9-1, which we took as an example, in the program “ImageJ” and changed the type to 8-bit. The next step is adjusting the threshold. The program allows an automatically threshold, but for a better analysis it does be done manually. Figure 1 shows the converted image. Other programs for example MATLAB or ArcGIS can be used as well.
Summary of Chapters
I. Description of the used method: This chapter outlines the preparation and digital processing workflow, including software-based thresholding, to visualize subgrain boundaries in halite samples.
II. Calculation Results of all Pictures: This section presents the aggregated quantitative data for all analyzed rock salt samples, summarized in tables and particle distribution diagrams.
III. Error calculation: This chapter discusses the limitations of the measurement process, specifically identifying gas bubbles and cracks as primary sources of statistical noise.
IV. Palaeo-stress: This section details the conversion of pixel-based measurements into micrometers and applies established geological literature to estimate the corresponding palaeo-stress in MPa.
V. References: This chapter lists the external sources and literature used to validate the findings and support the palaeo-stress comparison.
Keywords
Halite, Subgrain Size, Piezometry, Microstructural Analysis, ImageJ, Triassic, Rock Salt, Palaeo-stress, Grain Boundaries, Thresholding, Image Processing, Error Propagation, Crystal Structure, Optical Isotropy, Geomechanics
Frequently Asked Questions
What is the primary focus of this study?
The study focuses on the microstructural analysis of Triassic halite to determine subgrain sizes and relate these to historical stress conditions.
What are the central thematic fields?
The work covers structural geology, digital microstructural analysis, and geomechanics, specifically focusing on rock salt properties.
What is the core research question?
The research asks if subgrain size measurements derived from specific digital image processing techniques can reliably estimate palaeo-stress in halite.
Which scientific method is utilized?
The authors use digital image processing (ImageJ) to segment crystal boundaries, followed by statistical area calculations and stress estimation based on established empirical relationships.
What does the main body cover?
The main body covers the workflow of image preparation, the presentation of measurement results for various samples, the statistical evaluation of errors, and the final stress estimation.
Which keywords characterize this paper?
Key terms include Halite, Piezometry, Microstructural Analysis, ImageJ, and Palaeo-stress.
Why are standard deviations relatively high in the measurements?
The high standard deviation is attributed to noise introduced by non-grain features such as gas bubbles trapped under the thin section and cracks within the sample.
How is the transition from pixels to micrometers achieved?
The conversion is based on the known file size properties of the digital images (using an 8-bit conversion ratio) to estimate the physical scale of the measured grains.
Does this method allow for highly accurate palaeo-stress determination?
The authors conclude that due to significant error sources like bubbles and cracks, this specific method does not allow for a high-precision determination of palaeo-stress.
- Quote paper
- Amalia Aventurin (Author), 2013, Subgrain Size Piezometric on a Halite, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/272601
