Mineralogical and colour changes of quartz sandstones by heat

M. Hajpál, Á Török

Research output: Contribution to journalArticle

109 Citations (Scopus)

Abstract

Seven German and three Hungarian monumental sandstones have been tested in laboratory conditions to analyse the effect of heat. The studied quartz sandstones have a wide-range of cements and grain-sizes including silica-, carbonate-, clay- and ferrous mineral - cemented varieties of fine-, medium- to coarse-grained types. Cylindrical specimens were heated up to 150, 300, 450, 600, 750 and 900°C in an oven. The mineralogical and textural changes were recorded and compared by using microscopy, XRD, DTA-DTG and SEM. Colours and colour differences (a*, b*, L* values) were also measured and evaluated. Colour changes are related to mineral transformations. The most intense colour change is caused by the oxidation of iron-bearing minerals to hematite that takes place up to 900°C. When temperature increases the green glauconite becomes brownish while the chlorite changes to yellowish at first. The colour of burnt sandstone is not a direct indicator of burning temperature, since there are sandstones in which the burnt specimens are lighter and less reddish than the natural ones. Porosity increase is related to micro-cracking at grain boundaries (above 600°C) and within the grains (at and above 750°C) and mineral transformations. The clay mineral structure collapses at different temperatures (kaolinite up to 600°C, chlorite above 600°C) and leads to a slight increase in porosity. The most drastic change is observed in calcite cemented sandstones where the carbonate structure collapses at 750°C and CaO appears at 900°C. Subsequently it is transformed to portlandite due to absorption of water vapour from the air. This leads to the disintegration of sandstone at room temperature a few days after the heat shock.

Original languageEnglish
Pages (from-to)311-322
Number of pages12
JournalEnvironmental Geology
Volume46
Issue number3-4
DOIs
Publication statusPublished - Aug 2004

Fingerprint

Quartz
sandstone
quartz
Sandstone
Color
heat
Minerals
color
collapse structure
minerals
chlorite (mineral)
Carbonates
mineral
carbonates
porosity
chlorite
Bearings (structural)
Porosity
temperature
Kaolin

Keywords

  • Colour change
  • Heat
  • Mineralogy
  • Quartz
  • Sandstone

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)
  • Environmental Science(all)
  • Environmental Chemistry
  • Water Science and Technology

Cite this

Mineralogical and colour changes of quartz sandstones by heat. / Hajpál, M.; Török, Á.

In: Environmental Geology, Vol. 46, No. 3-4, 08.2004, p. 311-322.

Research output: Contribution to journalArticle

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