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Fougèrite
A valid IMA mineral species
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![Fe2+4Fe3+2(OH)12[CO3] · 3H2O](#"/photo-1023986.html"><img src="/image.pl?url=https%3a%2f%2fwww.mindat.org%2fimagecache%2f34%2fb5%2f00063610017272470983837.jpg&f=jpg&w=240" alt="00063610017272470983837.jpg" /></a><div><b>Fougères, France</b></div></div></div><div><div><span>Formula:</span><div class=){kind=link}
Colour:
Bluish green, green, green-black, blackish
Lustre:
Earthy
Crystal System:
Trigonal
Member of:
Name:
Named for "a forest near Fougères, Brittany, France", where the type material was collected.
The mineral formerly described as fougèrite has been found to be an intimate intergrowth of two phases with distinctFe2+:Fe3+ ratios. The phase withFe2+:Fe3+ = 2:1 retains the name fougèrite; that withFe2+:Fe3+ = 1:2 is defined as the new speciestrébeurdenite. Both belong to theFougèrite Group (Mills et al., 2012).
Fougèrite is unstable in air at normal conditions (Trolard et al., 2007); the green (or green-black, blackish), hexagonal, transparent platelets transform quickly into yellow-brown to brown, opaque, often poorly crystalline, brittle iron oxyhydroxides (limonite,goethite,lepidocrocite). Known previously as "Green Rust", mainly from iron-rich slags.
Varieties containing Zn retain their green colour and transparency (Blaß et al., 1997).
The characteristic blue-green colour (5BG6/1 in the Munsell system) of fougèrite has long been used as a universal criterion in soil classification to identify Gleysols (Trolard et al., 2007).
One of six minerals proposed to be essential for life emergence. Actually, one of two "vital" candidates due to "comprising precipitate membrane", the other one beingmackinawite (Russell & Pone, 2020).
Fougèrite is unstable in air at normal conditions (Trolard et al., 2007); the green (or green-black, blackish), hexagonal, transparent platelets transform quickly into yellow-brown to brown, opaque, often poorly crystalline, brittle iron oxyhydroxides (limonite,goethite,lepidocrocite). Known previously as "Green Rust", mainly from iron-rich slags.
Varieties containing Zn retain their green colour and transparency (Blaß et al., 1997).
The characteristic blue-green colour (5BG6/1 in the Munsell system) of fougèrite has long been used as a universal criterion in soil classification to identify Gleysols (Trolard et al., 2007).
One of six minerals proposed to be essential for life emergence. Actually, one of two "vital" candidates due to "comprising precipitate membrane", the other one beingmackinawite (Russell & Pone, 2020).