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Berthierine
A valid IMA mineral species - grandfathered
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![(Fe2+,Fe3+,Al)3(Si,Al)2O5(OH)4](#"/photo-268695.html"><img src="/image.pl?url=https%3a%2f%2fwww.mindat.org%2fimagecache%2f19%2f6a%2f00459640017271921546869.jpg&f=jpg&w=240" alt="00459640017271921546869.jpg" /></a><div><b>Pierre Berthier</b></div></div></div><div><div><span>Formula:</span><div class=){kind=link}
The chemically very pure berthierine described by Slack et al. (1992) contains nearly equal amounts of SiO2 and Al2O3.
Colour:
Dark olive green, yellowish green; reddish brown (Ti-bearing variety)
Lustre:
Pearly
Hardness:
2½
Specific Gravity:
3.06 (Calculated)
Crystal System:
Monoclinic
Member of:
Name:
Named in honor of Pierre Berthier (3 July 1782, Nemours, Seine-et-Marne, France – 24 August 1861, France), French chemist and mineralogist at the École des Mines, France. He was also Inspector of Mines during his career. He named a number of species includingchamosite,franklinite,halloysite, andnontronite. He is well-known for his study ofbauxite. The mineralberthierite is also named after him.
Type Locality:
A member of the Kaolinite-Serpentine group.
Common in unmetamorphosed marine sediments; in lateritic and polar soils, rarely as a hydrothermal phase.
"Berthierine is generally considered to be a metastable phase that inverts to 14 Å Fe-rich chlorite during diagenesis and metamorphism." (Slack et al., 1992). It was suggested that 7 Å berthierine undergoes a polymorphic transformation to 14 Å chlorite at temperatures of 25-100 °C.
1M and 1H polytypes are known.
Easily confused withchamosite.
Berthierine is difficult to recognise by normal XRD methods because the critical identifying feature, the absence of a 14 Å basal reflection, is commonly masked by a peak due to frequently admixed chlorite (Brindley, 1982; Slack et al., 1992).
Ahn & Peacor (1985) and Jahren & Aagaard (1989) have demonstrated that berthierine is generally more Fe-rich than chlorite, but that overlaps in chemistry occur. Thus, berthierine and chamosite cannot be distinguished on the basis of electron microprobe data alone.
Common in unmetamorphosed marine sediments; in lateritic and polar soils, rarely as a hydrothermal phase.
"Berthierine is generally considered to be a metastable phase that inverts to 14 Å Fe-rich chlorite during diagenesis and metamorphism." (Slack et al., 1992). It was suggested that 7 Å berthierine undergoes a polymorphic transformation to 14 Å chlorite at temperatures of 25-100 °C.
1M and 1H polytypes are known.
Easily confused withchamosite.
Berthierine is difficult to recognise by normal XRD methods because the critical identifying feature, the absence of a 14 Å basal reflection, is commonly masked by a peak due to frequently admixed chlorite (Brindley, 1982; Slack et al., 1992).
Ahn & Peacor (1985) and Jahren & Aagaard (1989) have demonstrated that berthierine is generally more Fe-rich than chlorite, but that overlaps in chemistry occur. Thus, berthierine and chamosite cannot be distinguished on the basis of electron microprobe data alone.