Ferrirockbridgeite

(Fe3+0.67◻0.33)2(Fe3+)3(PO4)3(OH)4(H2O)
IMA status
  • Approved
IMA symbol
Frck
Also known as
  • Ferrirockbridgeiet
  • IMA2018-065

Where it forms, where it's found

Geological setting

Oxidized zone of a granitic pegmatite. Highly oxidized alteration of triphylite.

Type locality
Palermo No. 1 Mine
  1. Groton
  2. Grafton County
  3. New Hampshire
  4. USA

43.7513°, -71.8896°

2recorded occurrences
Source · OpenStreetMap

Physical

Colour
Reddish-brown
Density
3.33 g/cm³

Optical

Optical type
Biaxial (-) · 2V measured = 78°
Refractive index
1.875 – 1.9
Surface relief
Very high
Principal indices
nα 1.875 · nβ 1.890 · nγ 1.900
Pleochroism
Visible

X = yellow brown, Y = olive brown, Z = dark olive green

Dispersion
Strong, with r > v
Notes

β calculated. Orientation: X = c, Y = a, Z = b. Absorption: Z > Y > X.

Michel-Lévy diagramhighlighted lineδ = 0.0250
Attainable Michel-Lévy rangeΔ ∈ [0, t·δmax]250 nm1st order
Δ = 0Δmax
Thin-section mosaic70 grains · random 3D orientations
PPLpleochroism per grain
XPLindependent extinctions · rotate the stage
Interference simulatorsingle grain · PPL ↔ XPL
PPLpleochroism only · colour blends on rotation
XPLinterference colour · extinct every 90°
Retardation250 nm
Order1st order
XPL colour

Crystallography

Crystal system
Orthorhombic
Cell parameters
a = 13.853(1) Å · b = 16.928(1) Å · c = 5.1917(5) Å
Ratio a:b:c
1 : 1.222 : 0.375
Z
4
Morphology

Blade-like crystals, flattened on (010) and elongated on [001].

Type-locality form

Radial fibrous crusts and masses. Compact intergrowths of reddish-brown blade-like crystals.

Comment

space group is Bbmm

Synonyms

  • Ferrirockbridgeiet
  • IMA2018-065

In other languages

German
Ferrirockbridgeit · IMA 2018-065

Classification

Strunz
10th ed.

8.BC.10

  • 8Phosphates, Arsenates, VanadatesClass
  • 8.BPhosphates, etc., with additional anions, without H2ODivision
  • 8.BCWith only medium-sized cations, (OH, etc.):RO4 > 1:1 and < 2:1Group
  • 8.BC.10FerrirockbridgeiteSpecies

Group, growth & confusion

In the same group
5 members

Literature, links & citation

Citations
  1. 2018Hålenius, U., Hatert, F., Pasero, M., Mills, S. J. (2018) CNMNC Newsletter 45, New minerals and nomenclature modifications approved in 2018. Mineralogical Magazine, 82 (5) 1225-1232 doi:10.1180/mgm.2018.160DOI: 10.1180/mgm.2018.160
  2. 2019Grey, Ian Edward, Kampf, Anthony R., Keck, Erich, Cashion, John D., MacRae, Colin M., Gozukara, Yesim, Shanks, Finlay L. (2019) Ferrirockbridgeite, (Fe3+0.67□0.33)2(Fe3+)3(PO4)3(OH)4(H2O), and the oxidation mechanism for rockbridgeite-group minerals. European Journal of Mineralogy, 31 (3) 585-594 doi:10.1127/ejm/2019/0031-2846 DOI: 10.1127/ejm/2019/0031-2846
Cite this entry
@misc{mineral2026,
  author    = {Mineral Index editorial board},
  title     = {Ferrirockbridgeite — Mineral Index},
  year      = {2026},
  url       = {https://mineralindex.org/minerals/ferrirockbridgeite-53168},
  note      = {Accessed 2026-05-11}
}