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Foretite, a new secondary arsenate mineral from the Cap Garonne Mine, France

S. J. Mills, A. R. Kampf, A. M. McDonald, G. Favreau and P. J. Chiappero
Foretite, a new secondary arsenate mineral from the Cap Garonne Mine, France
Mineralogical Magazine (June 2012) 76 (3): 769-775


Foretite, ideally Cu (sub 2) Al (sub 2) (AsO (sub 4) )(OH,O,H (sub 2) O) (sub 6) , is a new secondary arsenate mineral from the Cap Garonne mine, Var, France (IMA2011-100). It has also been identified at the Salsigne gold mine, Languedoc-Roussillon, France. Although it was identified as a potentially new mineral in 1993, a formal description has only been possible as a result of a new find in a chamber called Annex S located near the entrance of the Cap Garonne mine. Foretite occurs as pale sky blue to aqua aggregates, up to approximately 0.1 mm across, made up of minute plates no more than 20 mu m in length. It has a very pale blue streak. Individual crystals have a vitreous lustre and are transparent, whereas clusters appear translucent. The calculated density is 3.286 g cm (super -3) . The crystals are brittle, with an irregular fracture and have a hardness of approximately 3-4 on Moh's scale. Foretite is found in direct association with bariopharmacoalumite, cyanotrichite, parnauite, chalcophyllite and mansfieldite in an Al-rich assemblage which is presumed to have formed under acidic conditions. It is biaxial; the average refractive index measured in white light on aggregates of foretite crystals is 1.620(5). The empirical formula (based on 10 oxygen atoms per formula unit) is Cu (sub 1.94) (Al (sub 1.96) Fe (sub 0.04) ) (sub Sigma 2.00) (As (sub 0.84) S (sub 0.09) Si (sub 0.04) ) (sub Sigma 0.97) O (sub 10) H (sub 5.19) . Raman spectroscopy confirms the presence of OH and H (sub 2) O in the structure. Foretite is triclinic, space group P1i, with a = 6.969(9), b = 7.676(9), c = 8.591(11) Aa, alpha = 82.01(9), beta = 71.68(8), gamma = 102.68(8) degrees , V = 415(1) Aa (super 3) and Z = 2. The five strongest lines in the X-ray powder diffraction pattern [d in Aa, (I), (hkl)] are as follows: 7.307, (100), (010, 01i0); 3.141, (24), (200, 2i00); 2.818, (24), (22i0, 2i20); 4.519, (23), (111); 2.343, (22), (13i1). The mineral is named in honour of Dr Jean-Paul Foret, who co-founded the project that turned the Cap Garonne mine into a protected site and museum.

ISSN: 0026-461X
EISSN: 1471-8022
Serial Title: Mineralogical Magazine
Serial Volume: 76
Serial Issue: 3
Title: Foretite, a new secondary arsenate mineral from the Cap Garonne Mine, France
Affiliation: Museum Victoria, Geosciences, Melbourne, Victoria, Australia
Pages: 769-775
Published: 201206
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 10
Accession Number: 2012-092184
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N43°06'23" - N43°06'23", E06°01'23" - E06°01'26"
Secondary Affiliation: Natural History Museum of Los Angeles County, USA, United StatesLaurentian University, CAN, CanadaMuseum National d'Histoire Naturelle, FRA, France
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201248
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