Gypsum-anhydrite differentiation by SEM using the back-scattered electron-signal

Jordan, P.M.; Dueggelin, M.; Mathys, Daniel; Guggenheim, R.

doi:10.1306/d426777b-2b26-11d7-8648000102c1865d

Cited by 5 publications

(2 citation statements)

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“…Back-scattered electron (BSE) images permitted the differentiation of gypsum and anhydrite in the samples. In the BSE images these minerals show very pronounced grey-level differences: anhydrite is bright, and gypsum is dark [73]. In addition to the obtained images of the rock surface, EDS point and areal analysis of the elemental composition were also carried out.…”

Section: Laboratory Studiesmentioning

confidence: 99%

Petrographic Record and Conditions of Expansive Hydration of Anhydrite in the Recent Weathering Zone at the Abandoned Dingwall Gypsum Quarry, Nova Scotia, Canada

et al. 2021

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In the Dingwall gypsum quarry in Nova Scotia, Canada, operating in 1933–1955, the bedrock anhydrite deposits of the Carboniferous Windsor Group have been uncovered from beneath the secondary gypsum beds of the extracted raw material. The anhydrite has been subjected to weathering undergoing hydration (gypsification), transforming into secondary gypsum due to contact with water of meteoric derivation. The ongoing gypsification is associated with a volume increase and deformation of the quarry bottom. The surface layer of the rocks is locally split from the substrate and raised, forming spectacular hydration relief. It shows numerous domes, ridges and tepee structures with empty internal chambers, some of which represent unique hydration caves (swelling caves, Quellungshöhlen). The petrographic structure of the weathering zone has been revealed by macro- and microscopic observations. It was recognized that gypsification commonly starts from a developing network of tiny fractures penetrating massive anhydrite. The gypsification advances from the fractures towards the interior of the anhydrite rocks, which are subdivided into blocks or nodules similar to corestones. Characteristic zones can be recognized at the contact of the anhydrite and the secondary gypsum: (1) massive and/or microporous anhydrite, (2) anhydrite penetrated by tiny gypsum veinlets separating the disturbed crystals and their fragments (commonly along cleavage planes), (3) gypsum with scattered anhydrite relics, and (4) secondary gypsum. The secondary gypsum crystals grow both by replacement and displacement, and also as cement. Displacive growth, evidenced by abundant deformation of the fragmented anhydrite crystals, is the direct cause of the volume increase. Crystallization pressure exerted by gypsum growth is thought to be the main factor generating volume increase and, consequently, also the formation of new fractures allowing water access to “fresh” massive anhydrite and thus accelerating its further hydration. The expansive hydration is taking place within temperature range from 0 to ~30 °C in which the solubility of gypsum is lower than that of anhydrite. In such conditions, dissolving anhydrite yields a solution supersaturated with gypsum and the dissolution of anhydrite is simultaneous with in situ replacive gypsum crystallization. Accompanying displacive growth leads to volume increase in the poorly confined environment of the weathering zone that is susceptible to upward expansion.

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Section: Laboratory Studiesmentioning

confidence: 99%

Petrographic Record and Conditions of Expansive Hydration of Anhydrite in the Recent Weathering Zone at the Abandoned Dingwall Gypsum Quarry, Nova Scotia, Canada

et al. 2021

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“…11). The gypsum-anhydrite differentiation by SEM-BSE is very effective as the resulting images represent "atomic number contrast" which, in turn, depend on the density and atomic number of the elements present in the test specimen (Jordan et al, 1991). As the average atomic number of anhydrite is 11 and that of gypsum is 7, the two phases can be clearly distinguished by grey level differences, with anhydrite appearing brighter than gypsum.…”

Section: Sem-eds and Plm Observationsmentioning

confidence: 99%

Natural or Artificial? Multi-Analytical Study of a Scagliola from Estoi Palace Simulating Imperial Red Porphyry

Freire

Brito

Schlütter³

2016

Microsc Microanal

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In this paper the characterization of a gypsum plaster sample from the end of the 19th century simulating imperial red porphyry using a multi-analytical approach is presented and discussed. The results of X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TGA-DTA), physical and mechanical properties are summarized. In order to have further insight into the microstructure, polarized light microscopy (PLM), scanning electron microscopy coupled with energy dispersive X-ray spectrometer (SEM-EDS), and micro Raman spectroscopy analyzes were also made. They helped to clarify the main issues raised by the other complementary analytical techniques and allowed the establishment of interrelations between the different properties, providing important information about the materials, the skills, and the technological development involved in the art of imitating noble stones with gypsum pastes. This study also contributes to our knowledge concerning the preservation of these types of elements that are important in the context of European decorative arts and rarely reported in the literature.

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The celestite problem in gypsum Sr geochemistry: An evaluation of purifying methods of gypsiferous samples

Playà

Rosell

2005

Chemical Geology

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Gypsum-anhydrite differentiation by SEM using the back-scattered electron-signal

Cited by 5 publications

References 0 publications

Petrographic Record and Conditions of Expansive Hydration of Anhydrite in the Recent Weathering Zone at the Abandoned Dingwall Gypsum Quarry, Nova Scotia, Canada

Petrographic Record and Conditions of Expansive Hydration of Anhydrite in the Recent Weathering Zone at the Abandoned Dingwall Gypsum Quarry, Nova Scotia, Canada

Natural or Artificial? Multi-Analytical Study of a Scagliola from Estoi Palace Simulating Imperial Red Porphyry

The celestite problem in gypsum Sr geochemistry: An evaluation of purifying methods of gypsiferous samples

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