Plumbogummite
Plumbogummite, PbAl3(PO4)(PO3OH)(OH)6: lead aluminium phosphate of the crandallite group, hardness 4.5–5, density 4.01, from Caldbeck, Cornwall and Huelgoat.
Plumbogummite is PbAl3(PO4)(PO3OH)(OH)6, a lead aluminium phosphate of the crandallite group: hexagonal, hardness 4.5–5, density 4.01, usually as crusts and botryoidal masses, crystals to 5 mm. It is 35.65% lead by mass. A 20.00 g piece reads 15.01 g in water, at least 1.15 g heavier than crandallite, goyazite or gorceixite.
In short
- The species. The September 2026 IMA-CNMNC Master List lists plumbogummite as PbAl3(PO4)(PO3OH)(OH)6, status Rd, 1999 s.p., France. The Handbook of Mineralogy sheet, revised 2021, gives hexagonal R−3m, crystals to 5 mm but usually crusts, botryoidal, reniform or stalactitic; hardness 4.5–5; density 4.01; grayish white, grayish blue, yellowish, green or pale blue; white streak. Worked, it is 35.65% lead.
- The 15-gram line. Swapping lead for calcium makes the formula 40.37% heavier than crandallite’s while the cell grows only 3.77%. At 4.01 a 20.00 g piece reads 15.01 g in water; crandallite reads 12.81–13.42 g, goyazite 13.87 g and gorceixite 13.41–13.72 g at their sheets’ densities. A clean piece above 15 g is not one of those three.
- Documented failure: hinsdalite. Hinsdalite, PbAl3(SO4)(PO4)(OH)6, has the same lead fraction (35.65%) and a printed measured density of 3.65, so 14.52 g in water. But its own cell works out at 4.031, next to plumbogummite’s 4.053. The 0.49 g gap rests on one measured figure the cell does not support, so weight does not rule hinsdalite out.
- Documented failure: the Dry Gill analysis. The sheet’s Caldbeck analysis totals 94.1 and carries 4.80% CO2. Recast to 2 tetrahedral cations it holds only 1.326 P and 0.597 C, far from the formula. The sheet’s third reference is Grey et al. (2011), “Carbon incorporation in plumbogummite-group minerals”.
- Where it is found. Huelgoat, Finistère, France; Roughton Gill, Red Gill and Dry Gill, Caldbeck Fells; Wheal Gorland and other mines in Cornwall; Leadhills and Wanlockhead; Spain, the Czech Republic, the USA and Australia. Questions about lead and health are routed to toxic minerals in a collection; nothing here is health or safety advice.
| Mineral and IMA formula | Large cation | Pb, wt% | Density, measured (sheet) | Density from cell, worked | 20.00 g in water | Group as the sheet prints it |
|---|---|---|---|---|---|---|
| Plumbogummite, PbAl3(PO4)(PO3OH)(OH)6 | Pb | 35.65 | 4.01 (calc. [4.08]) | 4.053 | 15.01 g | Crandallite group |
| Crandallite, CaAl3(PO4)(PO3OH)(OH)6 | Ca | 0 | 2.78–3.04 | 2.996 (worked; as on the crandallite page) | 12.81–13.42 g | Crandallite group |
| Goyazite, SrAl3(PO4)(PO3OH)(OH)6 | Sr | 0 | 3.26 | 3.258 (worked; as on the crandallite page) | 13.87 g | Crandallite group |
| Gorceixite, BaAl3(PO4)(PO3OH)(OH)6 | Ba | 0 | 3.036–3.185 | 3.422 (worked; as on the crandallite page) | 13.41–13.72 g | Alunite supergroup, plumbogummite group |
| Hinsdalite, PbAl3(SO4)(PO4)(OH)6 | Pb | 35.65 | 3.65 | 4.031 | 14.52 g | Beudantite group |
| Pyromorphite, Pb5(PO4)3Cl | Pb | 76.38 | 7.04 | — | 17.16 g | Apatite group |
What is plumbogummite? Its formula and group
The lead member of a four-row formula. The September 2026 IMA-CNMNC Master List lists plumbogummite as PbAl3(PO4)(PO3OH)(OH)6, status Rd (redefined), 1999 s.p., France, with Mineralogical Magazine 75 (2011), 145 as its second reference. The live crandallite page shows by script that four IMA rows share the shape XAl3(PO4)(PO3OH)(OH)6, with calcium, strontium, barium or lead; this page agrees and does not repeat its A-cation ledger. With Pb 207.2, Al 26.98, P 30.97, O 15.999 and H 1.008, the formula mass is 581.13 and lead is 35.65%, aluminium 13.93% and phosphorus 10.66% by mass.
Two group names, both quoted. The Handbook of Mineralogy plumbogummite sheet, revised 8/12/2021, prints “Mineral Group: Crandallite group.” The gorceixite sheet, revised 12/8/2020, prints “Alunite supergroup, plumbogummite group.” This page, like the crandallite page, quotes both and does not choose. The plumbogummite sheet’s ideal column, PbO 38.41, Al2O3 26.32, P2O5 24.42 and H2O 10.85, is reproduced by the script to within 0.01.
How heavy is plumbogummite? The 15-gram line
Lead changes the weight, not the box. Plumbogummite’s cell, a = 7.017 and c = 16.75 Å, is only 3.77% larger than crandallite’s, but its formula is 40.37% heavier. Worked, three formula units in 714.3 ų give 4.053, near the sheet’s bracketed [4.08], and the sheet’s measured density is 4.01. A 20.00 g piece therefore reads 15.01 g suspended in water. Crandallite reads 12.81 to 13.42 g, goyazite 13.87 g and gorceixite 13.41 to 13.72 g, the figures on the crandallite page. The nearest is goyazite, 1.15 g lighter. The weighing method is at how to measure specific gravity at home.
Documented failure: hinsdalite. The lead aluminium sulfate-phosphate hinsdalite, PbAl3(SO4)(PO4)(OH)6 (IMA Rd, 1987 s.p., USA), has the same lead fraction, 35.65%. Its Handbook sheet prints a measured density of 3.65, beudantite group, so a 20.00 g piece would read 14.52 g, 0.49 g lighter than plumbogummite. But its own cell, a = 7.029 and c = 16.789 Å, works out at 4.031. A gap that the cells do not support cannot carry a decision, so the line separates plumbogummite from the calcium, strontium and barium members and not from hinsdalite. Matrix pulls any reading toward the matrix, and the sheet gives the usual habit as crusts.
What do the plumbogummite analyses show?
Ivanhoe reproduces the shape. The sheet’s analysis (1), Ivanhoe mine, Tennant Creek district, Northern Territory, Australia, by electron microprobe with H2O by difference, prints SO3 0.67, P2O5 22.47, As2O5 0.04, Al2O3 25.45, CuO 0.92 and PbO 38.90, leading to Pb1.02Cu0.07Al2.92[(PO4)1.85(SO4)0.05]Σ=1.90(OH)5.29·0.73H2O. Recast by script to 2 tetrahedral cations (P + As + S), it gives Pb 1.071 and Al 3.069: the same proportions as the printed formula, whose 1.02 Pb to 1.90 tetrahedral cations is a ratio of 0.537 against the script’s 0.536. Lead is 36.11% by mass.
Documented failure: Dry Gill. Analysis (2), Dry Gill mine, Caldbeck Fells, Cumbria, by electron microprobe, prints P2O5 17.2, As2O5 1.53, Al2O3 21.3, CaO 0.20, PbO 36.0 and CO2 4.80, total 94.1, and the sheet notes that IR confirms carbonate. Recast to 2 tetrahedral cations including carbon, it holds 1.326 P, 0.073 As and 0.597 C, with 0.882 Pb and 2.286 Al. That is not the ideal formula, and the low total leaves the shortfall unexplained. The sheet’s reference (3) is Grey, Shanks, Wilson, Mumme and Birch (2011), “Carbon incorporation in plumbogummite-group minerals”, Mineral. Mag. 75, 145–158; the page reports the arithmetic and does not go beyond that title.
Where is plumbogummite found? Huelgoat, Caldbeck and Cornwall
Distribution, as printed. In France, Huelgoat, Finistère. In England, Roughton Gill, Red Gill, Dry Gill and other mines, Caldbeck Fells, Cumbria; in Cornwall, Wheal Gorland, Gwennap; the Penberthy Croft mine, St. Hilary; the Buttern Hill placers, Altarnum; and Wheal Alfred, Gwinear. In Scotland, Leadhills, Lanarkshire, and Wanlockhead, Dumfriesshire. The Horcajo mines, Spain; Moldava, Czech Republic. In the USA, the Canton mine, Georgia; the Tyrone mine, Santa Rita, and the Mex-Tex mine, near Bingham, New Mexico; the Hahns Peak district, Colorado; the Copper Cities deposit, Arizona; the Silver Coin and San Rafael mines, Nevada. In Australia, the Ivanhoe mine, Northern Territory; the Teutonic Bore deposit, Western Australia; and Broken Hill, New South Wales. The sheet names no locality in China. Several other minor localities are known.
With pyromorphite. The Occurrence field reads “An uncommon secondary mineral in the oxidized zone of lead deposits”, and the associates are pyromorphite, mimetite, duftite, cerussite, anglesite and wulfenite, pyromorphite first. Collectors search for plumbogummite after pyromorphite; the sheet does not print the word pseudomorph, and no source fetched for this page describes that replacement, so this page makes no claim about it. The general idea is on what is a pseudomorph. More phosphates are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.
Name and lead. The name is from the Latin for lead and gum, which it may resemble; type material is at the Natural History Museum, Paris. The sheet marks no type locality and the IMA list gives France (see what is a type locality). Questions about lead and health are routed to toxic minerals in a collection; nothing here is health or safety advice.