Diaboleite
Diaboleite, CuPb2Cl2(OH)4: tetragonal deep-blue square plates to 2 cm, hardness 2.5, density 5.42, pale blue streak; Mendip Hills, Somerset, and Tiger, Arizona.
Diaboleite is a lead copper chloride hydroxide, CuPb2Cl2(OH)4 on the IMA list (Rn, 2007): tetragonal deep-blue square plates to 2 cm, hardness 2.5, density 5.42, streak pale blue, perfect {001} cleavage. Its two analyses give 1.98 and 2.02 lead per copper, the formula’s two to one. The Handbook names Higher Pitts Farm and Merehead quarry, Somerset.
In short
- The two-to-one check. The September 2026 IMA-CNMNC Master List writes diaboleite CuPb2Cl2(OH)4; the Handbook of Mineralogy sheet writes Pb2CuCl2(OH)4, the same atoms. Its Mendip Hills analysis recasts to Pb2.10Cu1.06Cl2.00(OH)4.44 and its Tiger, Arizona analysis to Pb1.98Cu0.98Cl1.98(OH)4.01: 1.98 and 2.02 lead per copper.
- The Pb-per-Cu ladder. A script over the IMA list finds 4 rows built only of lead, copper, chlorine, oxygen and hydrogen. Lead per copper: cumengeite 1.05, pseudoboleite 1.29, diaboleite 2.00, chloroxiphite 3.00. boleite (1.08) carries potassium and silver and falls outside the four. Two to one is diaboleite’s alone among them.
- Documented failure: blue is not a test. Boleite, pseudoboleite and diaboleite are all blue lead copper chlorides; their in-water weights, 16.04, 15.88 and 16.31 g for 20.00 g, sit within 0.43 g. The optics differ: boleite isotropic, n 2.05; pseudoboleite uniaxial, ω 2.03, ε 2.00; diaboleite uniaxial, ω 1.98, ε 1.85, a birefringence of 0.13.
- Where. In England the Distribution field names the Higher Pitts Farm, Mendip Hills, the Merehead quarry near Shepton Mallet, Somerset, and Padstow Consols, Cornwall. Exceptional crystals come from the Mammoth-St. Anthony mine, Tiger, Arizona. It also forms in slag, at Richelsdorf, Baratti Beach and Laurium.
- Lead. Worked from the formula, diaboleite is 67.18% lead by mass. It is a lead mineral; lead is covered on toxic minerals in a collection and is galena toxic. This page is not safety or health advice.
| Species or analysis | IMA formula or recast | Pb per Cu | System | Hardness | Density (meas.) | 20.00 g in water | Optics | Streak |
|---|---|---|---|---|---|---|---|---|
| Diaboleite (IMA) | CuPb2Cl2(OH)4 | 2.00 | Tetragonal | 2.5 | 5.42 | 16.31 g | Uniaxial (−); ω 1.98, ε 1.85 | Pale blue |
| Diaboleite, Mendip Hills | Pb2.10Cu1.06Cl2.00(OH)4.44 | 1.98 | — | — | — | — | — | — |
| Diaboleite, Tiger, Arizona | Pb1.98Cu0.98Cl1.98(OH)4.01 | 2.02 | — | — | — | — | — | — |
| Chloroxiphite | Pb3CuO2Cl2(OH)2 | 3.00 | Monoclinic | 2.5 | 6.76 to 6.93 | 17.04 to 17.11 g | Biaxial (−); α 2.16, γ 2.25 | Pale yellowish green |
| Pseudoboleite | Pb31Cu24Cl62(OH)48 | 1.29 | Tetragonal | 2.5 | 4.85 | 15.88 g | Uniaxial (−); ω 2.03, ε 2.00 | Not printed |
| Cumengeite | Pb21Cu20Cl42(OH)40(H2O)6 | 1.05 | No sheet (HTTP 404) | — | — | — | — | — |
| Boleite (outside the four: K, Ag) | KAg9Pb26Cu24Cl62(OH)48 | 1.08 | Cubic | 3 to 3.5 | 5.054 | 16.04 g | Isotropic; n 2.05 | Blue, with greenish tint |
What is diaboleite? A blue lead copper chloride
Diaboleite is CuPb2Cl2(OH)4 on the September 2026 IMA list, status Rn, 2007 s.p. The list’s key defines Rn as an existing mineral renamed during the IMA era; its first reference is Mineralogical Magazine 20 (1923), 67, and its country column reads United Kingdom. The Handbook of Mineralogy diaboleite sheet writes the formula Pb2CuCl2(OH)4 and derives the name from the Greek for separate from, and the related mineral boleite. The chloroxiphite sheet spells it diabolite in its association line; a whole-line scan finds no diabolite on the IMA list.
On the sheet. Tetragonal, point group 4mm, space group P4mm, as crystals tabular on {001} with a square or octagonal outline and vicinal forms, rarely showing pyramidal hemihedralism, to 2 cm, in subparallel aggregates, and massive. Cleavage {001} perfect, fracture conchoidal, brittle. Hardness 2.5; density 5.42 measured, 5.48 calculated. Deep blue, pale blue in transmitted light, streak pale blue, adamantine and pearly on cleavages. Uniaxial (−), ω 1.98, ε 1.85. The sheet’s text layer is a scan; these values were read from the rendered page.
Its chemistry, worked. On standard atomic weights the formula is 67.18% lead, 10.30% copper and 11.49% chlorine by mass. As oxides it returns the sheet’s ideal column (3) to within 0.01: CuO 12.89 against 12.90, PbO 72.36, Cl 11.49, H2O 5.84, less 2.59 for the oxygen equivalent of chlorine.
Why is the lead-to-copper ratio the useful number?
Because it is what the analyses agree on. The sheet’s Mendip Hills analysis recasts to Pb2.10Cu1.06Cl2.00(OH)4.44 and the Tiger analysis to Pb1.98Cu0.98Cl1.98(OH)4.01. Lead per copper is 1.98 and 2.02: each within 0.02 of the formula’s 2. Chlorine per copper is less tidy, 1.89 and 2.02, and the Mendip hydroxyl, 4.44, is 0.44 above the ideal.
The Pb-per-Cu ladder. By script, the IMA list has 4 rows built only of Pb, Cu, Cl, O and H: cumengeite (1.05 lead per copper), pseudoboleite (1.29), diaboleite (2.00) and chloroxiphite (3.00). The silver test that separates boleite is on the boleite page and is not repeated here. On this ladder an analysis near two to one reads diaboleite and one near three to one reads chloroxiphite, the green blade that shares the Mendip pods.
How do you tell diaboleite from the other Mendip and Boleo minerals?
Colour and habit first, then optics. Chloroxiphite is dull olive-green to pistachio-green in bladed crystals, and mendipite colourless to white; the density key for the three Mendip oxychlorides is on the mendipite page. Among the blue lead copper chlorides, weight fails: 20.00 g reads 16.31 g in water as diaboleite, 16.04 g as boleite and 15.88 g as pseudoboleite, on how to measure specific gravity at home.
Where the optics separate them. On their sheets boleite is cubic and isotropic, n 2.05; pseudoboleite is uniaxial with ω 2.03 and ε 2.00, a birefringence of 0.03; diaboleite is uniaxial with ω 1.98 and ε 1.85, 0.13. A square diaboleite plate with perfect {001} cleavage is also not a cube. The pseudoboleite sheet adds that its X-ray pattern may totally obscure that of intergrown boleite, so a mixed piece is a laboratory matter.
Where is diaboleite found? Mendip, Cornwall, Arizona and slag
The Distribution field names, in England, the Higher Pitts Farm, Mendip Hills, and the Merehead quarry, near Shepton Mallet, Somerset, and Padstow Consols, Padstow, Cornwall. In Germany the Christian-Levin mine near Essen, and Richelsdorf, Hesse, in slag; Baratti Beach, Tuscany, in slag; Laurium, Greece, in slag. In the USA, exceptional crystals from the Mammoth-St. Anthony mine, Tiger, and the Rowley mine, Arizona. Also the Anarak district, Neyband and Tabas, Iran; Moolyella and the Anticline prospect, Western Australia; the Santa Ana mine, Caracoles, Chile; and the Kopet-Dag Range.
Two settings. The occurrence line gives oxidized manganese ores in the Mendip Hills, deeply oxidized Pb–Cu ores at Tiger, and slag exposed to seawater. The Mendip associates it lists are chloroxiphite, hydrocerussite, mendipite and cerussite; at Tiger, boleite, wherryite, hydrocerussite, leadhillite, phosgenite, caledonite, atacamite, paratacamite and cerussite. The sheet marks no type locality and this page claims none; type material is at the Natural History Museum, London, 1923,521, and the National Museum of Natural History, Washington, D.C., 94813.
The rest of the reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.