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Iron (hydr)oxide nanocrystals in raw and burnt sienna pigments

Andrea Manasse and Marcello Mellini
Iron (hydr)oxide nanocrystals in raw and burnt sienna pigments
European Journal of Mineralogy (December 2006) 18 (6): 845-853


The mineral pigments known as bolar earths consist mostly of iron (hydr)oxides and the two pigments raw and burnt sienna, yellow and red-brown, respectively, which differ following thermal processing of the raw material. Sixteen samples of bolar earths from a quarry in Monte Amiata and from a museum were studied by XRD, SEM-EDS, TEM-EDS, TG-DTA and FTIR spectrometry. The raw sienna is yellow to brown and consists mainly of goethite, whereas the burnt sienna is red and contans hematite as a result of heating the goethite to approximately 270 degrees C. Chemical analyses report dominant Fe (sub 2) O (sub 3) (53.5-71.5 wt %) with minor SiO (sub 2) (3.0-24.7 wt %) and Al (sub 2) O (sub 3) (0.8-7.1 wt %). All the samples have a high content of As (mean value 5.6 wt % As (sub 2) O (sub 5) ). The goethite and hematite occur as finely dispersed nanocrystals, 2-10 and 10-40 nm, respectively, in size. They are enclosed in minor amorphous silica matrix, with As adsorbed on the nanoparticles. Due to the high As content, the ochre used to produce raw and burnt sienna is an effective natural sink for arsenic.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 18
Serial Issue: 6
Title: Iron (hydr)oxide nanocrystals in raw and burnt sienna pigments
Affiliation: Universita di Siena, Dipartimento di Scienze della Terra, Siena, Italy
Pages: 845-853
Published: 200612
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 37
Accession Number: 2007-017137
Categories: General geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
N42°19'60" - N44°19'60", E09°40'00" - E12°25'00"
N42°52'60" - N42°52'60", E11°37'00" - E11°37'00"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 200710
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