Beraunite

What is beraunite? A ferric iron phosphate since 2021

On the IMA list, Fe3+6(PO4)4O(OH)4(H2O)4·2H2O, status Rd, 2021 s.p., country Czech Republic. Rd means redefined during the IMA era, and s.p. marks the year of the approved action. The 2022 paper behind it writes the same formula as Fe3+6(PO4)4O(OH)4·6H2O and reports that CNMNC proposal 21D discredited the name eleonorite and accepted that formula for beraunite. On standard atomic weights it has a formula mass of 907.07 and is Fe2O3 52.81%, P2O5 31.30% and H2O 15.89%.

On the Handbook sheet. The Handbook of Mineralogy beraunite sheet still prints the earlier formula, Fe2+Fe3+5(PO4)4(OH)5·6H2O. It records a monoclinic mineral, point group 2/m, in crystals tabular on {100} and elongated along [010], to 1 cm, striated on {100} parallel to [010], and in coarse radially fibrous aggregates, globular or discoidal masses and crusts. Twinning on {100}, may be interpenetrant. Cleavage on {100} good; hardness 3 to 4; density 2.8 to 3.08 measured. Lustre vitreous, pearly on cleavages, resinous on fractures. Biaxial (+), may be biaxial (−), α 1.707 to 1.775, β 1.735 to 1.786, γ 1.738 to 1.820.

Positive control. Worked on standard atomic weights, the old formula gives P2O5 31.26, Fe2O3 43.96, FeO 7.91 and H2O 16.86, against the sheet’s ideal column of 31.26, 43.97, 7.91 and 16.86. With the sheet’s greenish black cell and Z = 4 it also gives the printed calculated density, 2.894. So the sheet’s density and ideal column both belong to the composition the IMA now calls ferroberaunite.

Is my beraunite really ferroberaunite? The ferrous check

Count the ferrous iron per four phosphorus. In the IMA formulas, beraunite has 0 Fe2+ and ferroberaunite has 1, with 6 iron atoms in each. Recast from oxide weights, the sheet’s Middletown, New Jersey, analysis (P2O5 30.17, Fe2O3 54.41, FeO 1.92, H2O 13.45) gives 0.25 Fe2+ and 6.41 Fe3+ per 4 P, so 3.8% of its iron is ferrous. The total, 6.66 iron atoms, is above the formula’s 6, which is what a bulk analysis of partially oxidized material can do.

Its limit. Vrtiška and others (2022) describe the difference as structural: their site M1 is occupied by Fe3+ in beraunite and by Fe2+ in ferroberaunite, and they give beraunite from the type locality the lower symmetry Cc, where earlier work had C2/c. A wet analysis or a colour does not show what sits on M1, so the ferrous check is a reason to question an old label, not a way to settle it. The paper gives the empirical formula of the original Hrbek specimen as (Fe3+5.76Al0.15Zn0.01)Σ5.92(PO4)4.00O0.99(OH)3.77·6H2O.

What ferroberaunite is. The IMA list gives Fe2+Fe3+5(PO4)4(OH)5(H2O)4·2H2O, approved 2021-036, country United Kingdom, first reference Mineralogical Magazine 86 (2022), 363. The paper’s reference list titles that description as from the Gravel Hill mine, Perranzabuloe, Cornwall, which the beraunite sheet’s Distribution field also names. This page says nothing further about ferroberaunite.

What colour is beraunite? The documented failure

The two sources disagree, and the newer one explains why. The Handbook sheet reads dull greenish to greenish brown when fresh, may be colour banded; reddish brown to hyacinth-red, blood-red on exposure, with an olive-drab streak when fresh turning yellow to brownish yellow. The 2022 paper describes the type material as hyacinth red, dark red or red-brown, with a light orange-red streak, in prismatic crystals up to 0.2 × 0.5 × 3 mm and radial clusters up to 6 mm, with black goethite, olive-green to dark green dufrénite and yellow to orange cacoxenite.

The paper’s reading. It quotes Breithaupt’s 1840 description, dark hyacinth red, and says no specimen from the type locality in the Freiberg or Prague collections shows green or dark blue-green beraunite. It names the structurally related dark-green phosphate with Fe2+ on M1, until then called beraunite, as ferroberaunite. A green specimen labelled beraunite before 2021 is therefore exactly the case the ferrous check is for.

A second failure: the type-material number. The sheet gives the type material as Mining Academy, Freiberg, Germany, 21359. The 2022 paper says the original Breithaupt specimen carries inventory number 21519, that 21359 is incorrect and refers to a later piece, and that a neotype is held in the National Museum, Prague, P1N 18943. Read the sheet’s catalogue line with that correction.

Where is beraunite found? The sheet’s localities

Settings. The sheet calls it a component of bog iron ores; a cement in clays, sands and bone material; and an alteration product of triphylite in granite pegmatites. Its associates are vivianite, dufrénite, rockbridgeite, cacoxenite, wavellite, ferrostrunzite, ferristrunzite, frondelite, huréaulite, mitridatite, stewartite, laueite, leucophosphite, triphylite and “limonite”. How such sequences are read on a specimen is on what is mineral paragenesis and how do mineral specimens form.

Distribution, as printed. The Hrbek mine at St. Benigna, near Beroun, Czech Republic. In Germany, the Eleonore and Rotläufchen iron mines near Giessen, Hesse, and Hühnerkobel near Zwiesel, Hagendorf and the Kreuzberg, Pleystein, Bavaria. The Gravel Hill mine, Perranzabuloe, Cornwall, England. The Mangualde pegmatite near Mesquitela, Portugal. The Leveäniemi mine, Svappavaara, near Kiruna, Sweden. In the USA, the Palermo #1 and Fletcher mines near North Groton, New Hampshire; Raccoon Creek, Mullica Hill, New Jersey; the Hesnard and Big Chief mines, Pennington Co., South Dakota; the Foote mine near Kings Mountain, North Carolina. The Moculta phosphate quarry near Angaston, South Australia.

Type locality. The sheet lists Hrbek first but marks no type locality; the IMA list gives the Czech Republic, and the 2022 paper’s title calls its subject type material from the Hrbek Mine. The term is explained on what is a type locality. The rest of the phosphates are at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.

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