Liroconite
Liroconite, Cu2Al(AsO4)(OH)4(H2O)4: monoclinic copper aluminium arsenate, hardness 2 to 2.5, density 2.94 to 3.01, sky-blue lenses from Wheal Gorland, Cornwall.
Liroconite is a hydrated copper aluminium arsenate, Cu2Al(AsO4)(OH)4(H2O)4 on the IMA list (G, 1825, United Kingdom): monoclinic, sky-blue to verdigris-green lenses to 3.6 cm, hardness 2 to 2.5, density 2.94 to 3.01. A 20.00 g piece reads 13.20 to 13.36 g in water; the aluminium-free arsenates it grows with read 14.55 g or more.
In short
- The 14-gram line. The Handbook of Mineralogy liroconite sheet names five arsenates on its association line: olivenite, chalcophyllite, clinoclase, cornwallite and strashimirite. Worked as 20 − 20/D on their sheet densities, the four without aluminium in their September 2026 IMA-CNMNC Master List formulas read 14.55 g (strashimirite, calculated density) to 15.52 g (olivenite) in water for 20.00 g. Liroconite reads 13.20 to 13.36 g, at least 1.19 g lighter.
- Aluminium and water travel together here. Of the six, only liroconite and chalcophyllite carry aluminium, and worked from the IMA formulas they are also the wettest: 24.96% and 27.91% water by mass, against 3.18 to 10.32% for the other four. They are also the two lightest in water.
- Liroconite against chalcophyllite. Habit first: liroconite forms flattened octahedral or lenticular crystals; chalcophyllite forms hexagonal plates with a perfect micaceous cleavage. Optics: liroconite is biaxial, chalcophyllite uniaxial. Weight: 13.20 to 13.36 g against 12.51 to 12.57 g, a gap of 0.63 g.
- Documented failure. Two other arsenates the Handbook places at Wheal Gorland are not on liroconite’s association line and break the line: parnauite reads 13.53 g, only 0.17 g above liroconite, and pharmacosiderite 12.85 g, below it. The line is for liroconite’s own companions, not for every blue-green Cornish arsenate.
- Where. The Distribution field gives large crystals from Wheals Muttrell and Gorland, also Wheal Unity and the Ting Tang mine, near Gwennap, and Wheal Cock, St. Just, in Cornwall; Schwarzenberg and Sadisdorf, Saxony; Špania Dolina and L’ubietová, Slovakia; Beresovsk, Urals; and Sterling Hill, New Jersey, and Bisbee, Arizona.
| Species | Formula (IMA) | IMA status | Aluminium in formula | Water by mass, worked | Hardness | Density | 20.00 g piece in water | Colour (sheet) | Streak (sheet) |
|---|---|---|---|---|---|---|---|---|---|
| Liroconite | Cu2Al(AsO4)(OH)4(H2O)4 | G, 1825, United Kingdom | Yes | 24.96% | 2 to 2.5 | 2.94 to 3.01 | 13.20 to 13.36 g | Sky-blue, bluish green, verdigris-green, emerald-green | Pale blue to pale green |
| Chalcophyllite | Cu18Al2(AsO4)4(SO4)3(OH)24·36H2O | G, 1841, United Kingdom | Yes | 27.91% | 2 | 2.67 to 2.69 | 12.51 to 12.57 g | Emerald-green, grass-green, bluish green, blue | Pale green to bluish green |
| Strashimirite | Cu4(AsO4)2(OH)2·2.5H2O | A, 1967-025, Bulgaria | No | 10.32% | n.d. | n.d.; calc. 3.67 | 14.55 g (calc.) | White to pale green | Not printed |
| Cornwallite | Cu5(AsO4)2(OH)4 | G, 1847, United Kingdom | No | 5.43% | 4.5 | 4.17 | 15.20 g | Verdigris-green to blackish green, pale green | Not printed |
| Clinoclase | Cu3(AsO4)(OH)3 | G, 1830, United Kingdom | No | 7.10% | 2.5 to 3 | 4.38 | 15.43 g | Dark greenish blue to greenish black | Bluish green |
| Olivenite | Cu2(AsO4)(OH) | G, 1820, United Kingdom | No | 3.18% | 3 | 4.46 | 15.52 g | Olive-green, greenish brown, brown | Olive-green to brown |
| Parnauite (failure; not on the line) | Cu9(AsO4)2(SO4)(OH)10(H2O)4·3H2O | A, 1978-014, USA | No | 17.41% | About 2 | 3.09 | 13.53 g | Pale blue, green, dark green, blue-green | Not printed |
| Pharmacosiderite (failure; not on the line) | KFe3+4(AsO4)3(OH)4·6-7H2O | G, 1813, United Kingdom | No | 16.85 to 18.56% | 2.5 | 2.797 | 12.85 g | Olive-green, grass-green, emerald-green, honey-yellow, browns | Not printed |
What is liroconite? A copper aluminium arsenate
Liroconite is a hydrated copper aluminium arsenate, Cu2Al(AsO4)(OH)4(H2O)4 on the September 2026 IMA list, status G (grandfathered), 1825, with the United Kingdom as the country of first description. The Handbook of Mineralogy liroconite sheet writes the same composition as Cu2Al(AsO4)(OH)4·4H2O. It is monoclinic, point group 2/m, typically as crystals with a flattened octahedral or lenticular aspect, dominated by {110} and {011} and striated parallel to their intersections, with {001}, {010} and {100}, to 3.6 cm, alone and in sub-parallel groups; it may also be granular or massive. The forms were read from the rendered sheet, because the text layer drops overbars.
On the sheet. Cleavage on {110} and {011} is indistinct and the fracture uneven to conchoidal. Hardness is 2 to 2.5, measured density 2.94 to 3.01 and calculated 3.03. It is transparent to translucent, sky-blue, bluish green, verdigris-green or emerald-green, with a pale blue to pale green streak and a vitreous to resinous lustre; biaxial (−), α 1.612, β 1.652, γ 1.675. The name is from the Greek for pale and powder, for that streak.
Its chemistry, worked. On standard atomic weights the IMA formula has a formula mass of 433.08 and gives CuO 36.73%, As2O5 26.54%, H2O 24.96% and Al2O3 11.77%: exactly the ideal column the sheet prints. The sheet’s Cornish analysis reads As2O5 23.05 with P2O5 3.73 and Fe2O3 0.98, so some phosphorus stands in for arsenic in real material. Arsenic is 17.30% by mass; any question about handling arsenic minerals belongs on toxic minerals in a collection, and nothing on this page is health or safety advice.
How do you tell liroconite from the arsenates it grows with? The 14-gram line
A blue to green copper arsenate from liroconite’s assemblage that reads under 14 g in water for every 20.00 g is liroconite or chalcophyllite; olivenite, clinoclase, cornwallite and strashimirite all read 14.55 g or more. Worked as 20 − 20/D on the sheets’ densities: liroconite 2.94 to 3.01, 13.20 to 13.36 g; chalcophyllite 2.67 to 2.69, 12.51 to 12.57 g; strashimirite 3.67 (calculated; no measured density is printed), 14.55 g; cornwallite 4.17, 15.20 g; clinoclase 4.38, 15.43 g; olivenite 4.46, 15.52 g. The method is on how to measure specific gravity at home.
Method. The association names were read from the liroconite sheet’s Association field: olivenite, chalcophyllite, clinoclase, cornwallite, strashimirite, malachite, cuprite and “limonite”. Each was looked up on the September 2026 IMA list with a row parser; five have (AsO4) in their formula. Aluminium was then tested in each formula: chalcophyllite is the only one of the five with it. Water was worked from each formula, counting each OH as half a water molecule.
Why the pair is light. The two aluminous arsenates carry 24.96% (liroconite) and 27.91% (chalcophyllite) water by mass, against 10.32% for strashimirite, 7.10% for clinoclase, 5.43% for cornwallite and 3.18% for olivenite. The table shows the pattern; it does not prove a cause, and this page claims none. The 9 mm crystal ceiling that governs clinoclase is on the clinoclase page and is not repeated here.
Is it liroconite or chalcophyllite? Shape, optics, then weight
Liroconite makes lenses; chalcophyllite makes plates. The liroconite sheet gives flattened octahedral or lenticular crystals to 3.6 cm with indistinct cleavage. The chalcophyllite sheet gives hexagonal platy crystals to 1 cm, flattened on [0001], with a perfect micaceous {0001} cleavage and a pearly lustre on it. A crystal that splits into thin leaves is not liroconite on its sheet.
Optics and weight confirm it. Liroconite is biaxial (−) with γ − α = 0.063; chalcophyllite is uniaxial (−) with ω 1.618 and ε 1.552. A 20.00 g piece reads 13.20 to 13.36 g as liroconite and 12.51 to 12.57 g as chalcophyllite, 0.63 g apart. Hardness does not help: 2 to 2.5 against 2. Colour does not either: both sheets print bluish green and emerald-green. The two share the same Cornish mines; how chalcophyllite is told from its own sulphate-bearing companions is on the chalcophyllite page.
Where the 14-gram line fails
Parnauite and pharmacosiderite, both recorded at Wheals Gorland and Unity, Gwennap, on their own Handbook sheets, fall inside the band the line leaves to liroconite. Parnauite, Cu9(AsO4)2(SO4)(OH)10(H2O)4·3H2O, density 3.09, reads 13.53 g, only 0.17 g above liroconite’s top figure; its sheet describes lathlike crystals to 4 mm in bowties, rosettes and fans, and orthorhombic symmetry, not lenses. pharmacosiderite, KFe3+4(AsO4)3(OH)4·6-7H2O, density 2.797, reads 12.85 g, below liroconite; its sheet gives cubic crystals, isotropic, commonly anomalously biaxial.
So the line has a scope. It separates liroconite from the five arsenates its own sheet names as companions. A blue-green Gwennap arsenate outside that list needs habit and optics, and a small or massive one needs an analysis. turquoise, a copper aluminium phosphate and not an arsenate at all, reads 13.01 g at density 2.86, inside the same band.
Does liroconite lose water? What the sheet says
The liroconite sheet prints no dehydration, alteration or light-sensitivity statement, so this page gives none. Its Occurrence line reads: a rare secondary mineral in the oxidized zone of some copper deposits. The water figure above, 24.96%, is worked from the formula, not a measured loss. The chalcophyllite sheet does print indices for dehydrated material; that is covered on its page. Questions about storing arsenic minerals go to toxic minerals in a collection; this page gives no storage or handling advice.
Where liroconite is found
The Distribution field names, in England, large crystals from Wheals Muttrell and Gorland, also Wheal Unity and the Ting Tang mine, near Gwennap, and Wheal Cock, St. Just, Cornwall. In Germany: Schwarzenberg, Saxony; the Sadisdorf copper mine near Schmiedeberg; the Altväter samt Eschig mine near Sayda; and Ullersreuth near Hirschberg, Thuringia. Špania Dolina (Herrengrund) and L’ubietová (Libethen), Slovakia. The Preobrazhensky mine, Beresovsk, near Yekaterinburg, Middle Urals, Russia. In the USA, Sterling Hill, Ogdensburg, New Jersey, and Bisbee, Cochise Co., Arizona. The sheet’s X-ray pattern and analysis are both Cornish, but it marks no type locality; the IMA list gives the United Kingdom.
Weighing it. A 20.00 g liroconite reads 13.20 to 13.36 g in water; matrix pulls the reading towards that of the rock. The Cornish setting is on the Cornwall page and the rest of the reference section at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.