Boleite
Boleite is a deep blue cubic chloride of lead, silver and copper, hardness 3 to 3.5, named for Boleo, Mexico. How to tell it from pseudoboleite and cumengeite.
Boleite is a deep blue cubic chloride of lead, silver and copper, KPb26Ag9Cu24Cl62(OH)48: hardness 3 to 3.5, density 5.054, in cubic crystals to 2 cm. It is a secondary mineral named for Boleo, near Santa Rosalía, Mexico. Worked from its formula it is 8.88% silver by mass; pseudoboleite and cumengeite, its blue companions at Boleo, contain none.
In short
- The identity card, from the Handbook of Mineralogy sheet: cubic, deep Prussian blue to indigo, streak blue with a greenish tint, hardness 3 to 3.5, measured density 5.054, cleavage {001} perfect, isotropic with n = 2.05. Its crystals are cubes to 2 cm. A 2 cm cube, worked at 5.054, weighs 40.43 g.
- Two formulas, the same atoms. The Handbook writes KPb26Ag9Cu24Cl62(OH)48; the September 2026 IMA-CNMNC Master List writes KAg9Pb26Cu24Cl62(OH)48, status Rn, 1891, Mexico. Worked on standard atomic weights the formula is 49.26% lead, 13.95% copper and 8.88% silver, and the lead figure reproduces the sheet’s ideal column exactly.
- The silver test. Of the four blue lead-copper chlorides in the table below, boleite is the only one whose IMA formula contains silver. The sheet’s Boleo analysis has 12.03% AgCl, which is 9.05% silver, against 8.88% ideal.
- It grows with its look-alike. The sheet says boleite is commonly surficially layered with or overgrown by pseudoboleite, the two sharing {001}. Pseudoboleite is tetragonal, 2.5 in hardness and 4.85 in density. A scale cannot separate them: 16.04 g against 15.88 g in water for a 20.00 g piece.
- Boleo is the name, not the only place. The sheet gives exceptional crystals from the Amelia mine, Boleo, near Santa Rosalía, Baja California, then Arizona, Chile, Iran, Broken Hill and three Cornish localities, plus smelter slag leached by sea water at Laurium.
| Species | IMA formula | IMA status, year, country | Crystal system (Handbook) | Hardness | Density (measured) | Colour | Streak | Silver in the IMA formula | 20.00 g piece in water |
|---|---|---|---|---|---|---|---|---|---|
| Boleite | KAg9Pb26Cu24Cl62(OH)48 | Rn; 1891; Mexico | Cubic | 3 to 3.5 | 5.054 | Deep Prussian blue to indigo | Blue, with greenish tint | Yes: 8.88% by mass | 16.04 g |
| Pseudoboleite | Pb31Cu24Cl62(OH)48 | Rn; 2007 s.p.; Mexico | Tetragonal, pseudocubic | 2.5 | 4.85 | Indigo blue | Not printed | None | 15.88 g |
| Cumengeite | Pb21Cu20Cl42(OH)40(H2O)6 | Rn; 2007 s.p.; Mexico | No Handbook sheet fetched (HTTP 404) | Not quoted | Not quoted | Not quoted | Not quoted | None | Not worked |
| Diaboleite | CuPb2Cl2(OH)4 | Rn; 2007 s.p.; United Kingdom | Tetragonal | 2.5 | 5.42 | Deep blue | Pale blue | None | 16.31 g |
| Atacamite | Cu2Cl(OH)3 | G; 1797; Chile | Orthorhombic | 3 to 3.5 | 3.745 to 3.776 | Bright green, dark emerald-green to blackish green | Apple-green | None | 14.66 to 14.70 g |
What is boleite? A chloride of lead, silver and copper, worked
The formula was resolved in 2000. The sheet’s references end with Cooper and Hawthorne (2000), Boleite: resolution of the formula, KPb26Ag9Cu24Cl62(OH)48, Canadian Mineralogist 38. The September 2026 IMA-CNMNC Master List prints the same atoms in another order, KAg9Pb26Cu24Cl62(OH)48, with status Rn, 1891 and Mexico. The list defines Rn as renamed, an existing mineral renamed during the IMA era; we add nothing to that.
Worked on standard atomic weights, the formula mass is 10,936.45: lead 49.26%, chlorine 20.10%, copper 13.95%, silver 8.88%, potassium 0.36%. The sheet’s ideal column gives Pb 49.26 and AgCl 11.79, which is 8.87% silver; the two agree. Its Boleo analysis gives Pb 49.16 and AgCl 12.03, which is 9.05% silver.
It is a secondary mineral. The Occurrence field reads formed through reaction of chloride with primary sulfides in the oxidized zone of Pb–Cu deposits; in smelter slag immersed in and leached by sea water. The oxidised zone itself is described on what is a gossan.
Boleite or pseudoboleite? The silver test
The rule: silver in the formula means boleite, among the four blue lead-copper chlorides in the table. Method: we read the four IMA rows and searched each formula for Ag. Only boleite’s has it. Pseudoboleite, Pb31Cu24Cl62(OH)48, has none. The pseudoboleite sheet’s own Boleo analysis shows 1.6% AgCl, and the sheet deducts it as boleite before correcting to 100%. Its name, the sheet says, is from the Greek for false and boleite, as it was mistaken for that species.
In the hand, the crystal system helps. Boleite is cubic, in cubes to 2 cm, and isotropic. Pseudoboleite is tetragonal, pseudocubic, very rarely as single crystals, to 1 mm, and commonly overgrown on boleite. It is softer, at 2.5, and has a second cleavage, {101}, nearly perfect. Diaboleite, CuPb2Cl2(OH)4, is tetragonal too, deep blue with a pale blue streak, in tabular crystals to 2 cm. Cumengeite, the fourth, is on the boleite sheet’s list of associates at Boleo. Its Handbook sheet returned HTTP 404 when we fetched it, so this page quotes only its IMA row.
The scale does not help. A 20.00 g piece weighs 16.04 g in water as boleite, 15.88 g as pseudoboleite and 16.31 g as diaboleite: no pair is more than 0.43 g apart, and an overgrown crystal is a mixture anyway. The method is on how to measure specific gravity at home. Green atacamite, Cu2Cl(OH)3, 14.66 to 14.70 g, is separated by colour first.
Where boleite is found: Boleo, Arizona and Cornwall
Boleo first. The Distribution field opens In Mexico, exceptional crystals from the Amelia mine, Boleo, near Santa Rosalía, Baja California; also from an undefined locality in Sonora. The sheet’s Name field reads for the occurrence at Boleo, Mexico, and the IMA list gives Mexico as the country of first description. The sheet prints no [TL] marker, so this page names Boleo as the source of the name and the first description, as both sources do, and no more; the term is explained on what is a type locality. The associates at Boleo are pseudoboleite, cumengeite, atacamite, anglesite, cerussite, phosgenite and gypsum.
In the USA the sheet lists the Mammoth-St. Anthony mine, Tiger, and the Vekol mine, Pinal Co.; the Apache mine, Gila Co.; and the Rowley mine, Maricopa Co., Arizona; and Philipsburg, Montana. At the Mammoth-St. Anthony mine its associates include leadhillite, caledonite, matlockite and bideauxite.
In Britain it names three Cornish places: Tolcarne Beach, Newquay; Newporth Beach, near Falmouth; and the Porthilley mine, St. Minver. See Cornwall. Elsewhere: slag at Laurium, Greece, and at Juliushütte in the Harz; the Tchah Khuni mine, Iran; Broken Hill, New South Wales; and Huantajaya, Mantos Blancos and Caracoles in Chile. 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.
How big are boleite crystals? Cubes to 2 cm, weighed
The sheet’s size is 2 cm. Its habit field reads crystals cubic, to 2 cm, rarely modified by {111} and {011}, read from the rendered sheet. A 2 cm cube is 8 cm³; at 5.054 g per cm³ it weighs 40.43 g. The same cube of pseudoboleite would weigh 38.80 g, but the sheet gives pseudoboleite single crystals only to 1 mm.
Overgrowth, not twinning. The sheet records boleite as commonly surficially layered with or overgrown by pseudoboleite with mutually ∥ {001}: the two lattices share their {001} planes. Its powder-pattern note adds that boleite’s pattern may be totally obscured by the pattern of intergrown pseudoboleite. A label that reads boleite with pseudoboleite is describing exactly that. An overgrowth is neither a twin nor a pseudomorph; those are on mineral twinning explained and what is a pseudomorph.
The colour is diagnostic, the streak confirms. Deep Prussian blue to indigo in the hand, bluish green in transmitted light, and a blue streak with a greenish tint. The method is on how to use a streak plate.