Connellite
Connellite, Cu36(SO4)(OH)62Cl8·6H2O on the IMA list: hexagonal azure-blue needles to 2.5 cm, hardness 3, density 3.36 to 3.41, in a series with buttgenbachite.
Connellite is a copper sulfate chloride hydroxide, Cu36(SO4)(OH)62Cl8·6H2O on the IMA list (G, 1850): hexagonal azure-blue needles to 2.5 cm, hardness 3, density 3.36 to 3.41, streak pale greenish blue. The Handbook writes Cu36(SO4)2Cl6(OH)62·6–12H2O; its three analyses carry 7.51 to 7.8 chlorine per 36 copper, nearer the IMA’s 8.
In short
- Two formulas, one charge. The September 2026 IMA-CNMNC Master List writes connellite Cu36(SO4)(OH)62Cl8·6H2O; the Handbook of Mineralogy sheet writes Cu36(SO4)2Cl6(OH)62·6–12H2O. One sulfate (charge 2−) is traded for two chlorides (1− each), so both balance 36 copper at 72 charges. A script finds just 2 IMA rows that begin Cu36: connellite and buttgenbachite.
- The chloride count. The sheet’s three analyses, Grand Central mine, Utah; Czar mine, Bisbee; and Toughnut mine, Tombstone, carry 7.76, 7.51 and 7.8 chlorine per 36 copper. Each is within 0.49 of the IMA formula’s 8 and at least 1.51 from the Handbook’s 6. Their sulfate, 1.54 to 1.87, sits between the two formulas, and 0.22 to 0.52 nitrate fills the gap.
- The sulfate–nitrate switch. Buttgenbachite, connellite’s series partner, has (NO3)2 where connellite has (SO4). In the three connellite analyses sulfate carries 85.6% to 94.4% of the oxyanion charge; in the Likasi buttgenbachite analysis it carries 0%. An analysis decides the name.
- Documented failure: the hand cannot split them. Both are hexagonal, hardness 3, with a pale greenish blue streak. Measured densities 3.36 to 3.41 and 3.36 to 3.42 read 14.05 to 14.13 g and 14.05 to 14.15 g in water for 20.00 g. Both sheets name the Botallack mine, Bisbee and the Toughnut mine.
- Where. In Cornwall the Distribution field names the Wheals Gorland, Unity and Edward, the Botallack mine, others in St. Just and several other mines; also Southwick Cliffs, Scotland; the Britannia mine, Wales; Cap Garonne, France; Bisbee and Tombstone, Arizona; Tintic, Utah; and Broken Hill, New South Wales.
| Formula or analysis | Source | SO4 per Cu36 | NO3 per Cu36 | Cl per Cu36 | OH per Cu36 | H2O | Anion charge, worked | Cl nearer | Sulfate share of oxyanion charge | Reads as |
|---|---|---|---|---|---|---|---|---|---|---|
| Connellite, IMA formula | IMA list, September 2026 | 1 | 0 | 8 | 62 | 6 | 72 | — | 100% | Connellite |
| Connellite, Handbook ideal | Handbook sheet, column (4) | 2 | 0 | 6 | 62 | 12 (header 6–12) | 72 | — | 100% | Connellite |
| Grand Central mine, Tintic, Utah | Handbook analysis (1) | 1.87 | 0.22 | 7.76 | 60.28 | 6.26 | 72.00 | 8 (IMA), by 0.24 | 94.4% | Connellite |
| Czar mine, Bisbee, Arizona | Handbook analysis (2) | 1.54 | 0.52 | 7.51 | 60.89 | 6.66 | 72.00 | 8 (IMA), by 0.49 | 85.6% | Connellite |
| Toughnut mine, Tombstone, Arizona | Handbook analysis (3), structure | 1.6 | 0.4 | 7.8 | 60.6 | 6.7 | 72.00 | 8 (IMA), by 0.20 | 88.9% | Connellite |
| Buttgenbachite, IMA formula | IMA list, September 2026 | 0 | 2 | 8 | 62 | n (sheet ideal 10) | 72 | — | 0% | Buttgenbachite |
| Likasi, Congo | Buttgenbachite sheet analysis (1) | 0 | 4.00 | 6.80 | 61.20 | 7.92 | 72.00 | 6, by 0.80 | 0% | Buttgenbachite |
What is connellite? A copper sulfate chloride in blue needles
Connellite is Cu36(SO4)(OH)62Cl8·6H2O on the September 2026 IMA list, status G (grandfathered), 1850. The list’s first reference is Dana’s System of Mineralogy, 3rd edition (New York, 1850), and its country column reads USA. The Handbook of Mineralogy connellite sheet marks no type locality, and this page claims none. The name honours Arthur Connell (1794–1863), the Scottish chemist who first examined the mineral.
On the sheet. Hexagonal, point group 6/m 2/m 2/m, space group P63/mmc, as acicular prismatic crystals elongated and striated parallel to [0001], to 2.5 cm, commonly in tight radiating groups, and as fibrous, felted or crusty aggregates. Hardness 3; measured density 3.36 to 3.41, calculated 3.46. Translucent, azure-blue, blue in transmitted light, with a pale greenish blue streak and a vitreous lustre. Uniaxial (+), ω 1.724 to 1.738, ε 1.746 to 1.758; the ε symbol was read from the rendered sheet, because the text layer drops it. The sheet prints no cleavage and says nothing about light or water loss, so neither does this page.
Its chemistry, worked. On standard atomic weights the IMA formula gives CuO 74.77%, SO3 2.09%, Cl 7.41% and H2O 17.40%, less 1.67% for the oxygen equivalent of chlorine; copper is 59.73% by mass. The same arithmetic on the Handbook’s ideal, Cu36(SO4)2Cl6(OH)62·12H2O, returns its printed column to within 0.01: CuO 72.26 against 72.25, SO3 4.04, Cl 5.37, H2O 19.55. That check is the method’s positive control.
Why do the IMA list and the Handbook give different formulas?
They trade one sulfate for two chlorides, and both balance. Thirty-six copper ions carry 72 positive charges. The IMA formula balances them with one SO4 (2), 62 OH and 8 Cl; the Handbook with two SO4 (4), 62 OH and 6 Cl. Both sum to 72, so charge alone cannot choose between them.
The chloride count. The sheet prints three analyses, each already recast to 36 copper. Chlorine runs 7.76 (Grand Central mine, Tintic district, Utah), 7.51 (Czar mine, Bisbee, Arizona) and 7.8 (Toughnut mine, Tombstone, Arizona, from a crystal-structure analysis). Every one is within 0.49 of the IMA formula’s 8 and at least 1.51 away from the Handbook’s 6. Worked from each line, the anion charge is 72.00 in all three, so the analyses are internally consistent.
Where the count fails. On sulfate the same analyses read 1.87, 1.54 and 1.6: nearer the Handbook’s 2 than the IMA’s 1. Nitrate, 0.22 to 0.52, takes up the rest. Neither ideal formula reproduces a real analysis; the count says which way the chlorine leans, not that either formula is wrong. The sheet’s references include a 2003 single-crystal re-examination of the buttgenbachite–connellite series (Hibbs, Leverett and Williams, Mineralogical Magazine 67, 47), which this page has not read and does not paraphrase.
How do you tell connellite from buttgenbachite?
With an analysis, and with nothing else on the two sheets. The buttgenbachite sheet gives the nitrate partner as hexagonal acicular crystals to 1 mm, hardness 3, measured density 3.36 to 3.42, deep azure-blue with a pale greenish blue streak, uniaxial (+), ω 1.738, ε 1.752. Both X-ray patterns are printed as close to each other. Worked as 20 − 20/D, 20.00 g reads 14.05 to 14.13 g in water as connellite and 14.05 to 14.15 g as buttgenbachite; the method is on how to measure specific gravity at home.
The sulfate–nitrate switch. The IMA formulas differ in one place: (SO4) in connellite, (NO3)2 in buttgenbachite. Sulfate carries 94.4%, 85.6% and 88.9% of the oxyanion charge in the three connellite analyses, and 0% in the Likasi buttgenbachite analysis, which has 4.00 nitrate. The sheet’s reference list also names a sulphate-bearing buttgenbachite, Cu36Cl7.8(NO3)1.3(SO4)0.35, in which sulfate carries 35% of that charge. Material between the ends exists, so the label needs the numbers.
Locality does not settle it. Both sheets name the Botallack mine, St. Just, Cornwall; Bisbee; and the Toughnut mine, Tombstone. A Botallack label fits either species. Buttgenbachite crystals on its sheet reach 1 mm against connellite’s 2.5 cm, so a large spray is more likely connellite, but size is not a test.
Which blue copper minerals look like connellite?
The acicular blue ones, separated by weight and streak on their sheets. cyanotrichite, also sky-blue to azure and acicular, has density 2.74 to 2.95, 12.70 to 13.22 g in water for 20.00 g: at least 0.83 g lighter than connellite. azurite reads 14.70 g, 0.57 g heavier, and linarite 16.26 g. The streak key for these blue copper minerals is on the linarite page and is not repeated here; connellite’s streak is pale greenish blue. liroconite, the Cornish copper arsenate, reads 13.20 to 13.36 g.
Its companions on the sheet. The association field gives cuprite, spangolite, atacamite, botallackite, langite, malachite and azurite. Atacamite and botallackite are both Cu2Cl(OH)3 on the IMA list; spangolite, Cu6Al(SO4)(OH)12Cl·3H2O, carries both sulfate and chloride, like connellite. The arsenate–sulphate key across Cornish associates is on chalcophyllite, and the copper-to-arsenic ladder on cornubite.
Where is connellite found?
The Distribution field names, in England, the Wheals Gorland, Unity and Edward, the Botallack mine and others in St. Just, and several other mines in Cornwall; Southwick Cliffs, near Dalbeattie, Kirkcudbrightshire, Scotland; and the Britannia mine, Snowdonia, Wales. Also the Cap Garonne mine, Var, and Fontana Rossa, Corsica, France; the Sa Duchessa mine, Sardinia; Laurium, Greece, in slag; Weibing, Salzburg; the Clara mine, Black Forest; several mines at Bisbee and the Toughnut mine, Arizona; the Grand Central mine, Tintic, and the Gold Hill mine, Utah; Spring Creek and the Ediacara mine, South Australia; Broken Hill, New South Wales; and the Marharahara mine, New Zealand. The sheet adds that it is increasingly recognized from other minor localities.
Reading an old label. A Cornish locality is consistent with connellite but, as above, not proof against buttgenbachite at Botallack. The sheet’s X-ray pattern is from the Concordia mine, Cape Province, South Africa, a locality its Distribution field does not repeat. 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.