Antlerite
Antlerite is Cu3(SO4)(OH)4: an orthorhombic emerald-green copper sulfate, hardness 3.5, density 3.88, an ore at Chuquicamata. How it differs from brochantite.
Antlerite is Cu3(SO4)(OH)4, a basic copper sulfate: orthorhombic, emerald-green to blackish green, hardness 3.5, density 3.88, crystals to 2 cm, often fibrous. It carries 3 copper atoms per sulfur against brochantite’s 4, and the sheets’ Chuquicamata and Collahuasi analyses recast to 2.991 and 4.033. Its sheet calls it an important copper ore at Chuquicamata, Chile.
In short
- The species. The September 2026 IMA-CNMNC Master List lists antlerite as Cu2+3(SO4)(OH)4, status A, 1967 s.p., USA. The Handbook of Mineralogy sheet gives orthorhombic Pnam; crystals thick tabular on {010} or short prismatic, to 2 cm, and commonly fibrous; perfect {010} cleavage; hardness 3.5; density 3.88; emerald-green, blackish green or pale green, with a pale green streak. Worked, it is 53.74% copper.
- The copper-per-sulfur count. Antlerite has 3 Cu per sulfate, brochantite 4. Recast from oxide weights, the antlerite sheet’s Chuquicamata analysis gives 2.991 Cu per S and the brochantite sheet’s Collahuasi analysis 4.033. Hydrogen follows: 4.19 and 6.06 H per S against the formulas’ 4 and 6. An analysis decides the name in one division.
- Documented failure: the hand tests. Both sheets give emerald-green, blackish green and pale green, a pale green streak and a vitreous lustre. Hardness is 3.5 against 3.5–4. In water a 20.00 g piece reads 14.85 g as antlerite and 14.96 g as brochantite, 0.12 g apart. Nothing a collector can do at a bench separates them on the sheets’ numbers; the optic sign and an analysis can.
- Acid or low acidity. The two sheets read as a pair: antlerite forms “under highly acid conditions, especially in arid regions”; brochantite is “common in the oxidized zone of copper deposits, yet rarely an ore; formed under low acidity, principally in arid regions”. The antlerite sheet lists brochantite first among its associates.
- Where it is found. The Distribution field names the Antler mine, Bisbee and other Arizona mines; New Mexico, California, Nevada and Kennicott, Alaska; Puerto de Gomez, Mexico; Chuquicamata and Remolinos, Chile; Ober-Planitz, Saxony; Caldbeck Fells and several mines in Cornwall; and Capdella, Spain. Questions about copper compounds and health are routed to toxic minerals in a collection; nothing here is health or safety advice.
| Criterion | Antlerite | Brochantite | Does it separate them? |
|---|---|---|---|
| IMA formula | Cu2+3(SO4)(OH)4; A, 1967 s.p., USA | Cu4(SO4)(OH)6; A, 1980 s.p., Russia | Yes, by analysis |
| Copper per sulfur, ideal | 3 | 4 | Yes, by analysis |
| Copper per sulfur, sheet analysis | 2.991 (Chuquicamata, Chile; average of two) | 4.033 (Collahuasi, Chile; average of two) | Yes: each reproduces its formula |
| Copper by mass, worked | 53.74% | 56.20% | Only by analysis |
| Sulfur by mass, worked | 9.04% | 7.09% | Only by analysis |
| Crystal system | Orthorhombic, Pnam | Monoclinic, P21/a; twinning on {100} gives a pseudo-orthorhombic look | Weakly: the twins imitate it |
| Cleavage | {010} perfect; {100} poor | {100} perfect | Only on oriented crystals |
| Hardness (Mohs) | 3.5 | 3.5–4 | No |
| Density, measured | 3.88 | 3.97 | No |
| 20.00 g piece in water | 14.85 g | 14.96 g | No: 0.12 g apart |
| Colour and streak | Emerald-green, blackish green, pale green; streak pale green | Emerald-green, blackish green, pale green; streak pale green | No: printed identically |
| Optic sign and 2V | Biaxial (+), 53° | Biaxial (–), 77° | Yes, with a polarising microscope |
| Density from the cell, worked | 3.945 against the printed 3.93 | 3.981 against the printed 4.09 | Antlerite reproduces; brochantite does not |
| Occurrence wording | Uncommon; under highly acid conditions | Common, yet rarely an ore; under low acidity | Context only |
What is antlerite? Its formula and IMA status
A basic copper sulfate with three coppers. The September 2026 IMA-CNMNC Master List lists antlerite as Cu2+3(SO4)(OH)4, status A (approved), 1967 s.p., country USA; its reference is Canadian Mineralogist 27 (1989), 205. The Handbook of Mineralogy antlerite sheet writes Cu3(SO4)(OH)4 and cites the same paper: Hawthorne, Groat and Eby (1989), “Antlerite, Cu3SO4(OH)4, a heteropolyhedral wallpaper structure”. With Cu 63.546, S 32.06, O 15.999 and H 1.008, the formula mass is 354.72; copper is 53.74%, sulfur 9.04%, and the oxides come out at CuO 67.27, SO3 22.57 and H2O 10.16, the sheet’s ideal column to the second decimal.
What the sheet records. Orthorhombic, point group 2/m 2/m 2/m, space group Pnam, a = 8.244, b = 11.987, c = 6.043 Å, Z = 4. Crystals are thick tabular on {010}, equant or short prismatic along [001], with dominant {110} and another twenty-odd forms, to 2 cm; it is commonly fibrous and in cross-fiber veinlets, feltlike, or in granular or powdery lumps. Cleavage {010} perfect, {100} poor; brittle; hardness 3.5; density 3.88 measured, 3.93 calculated. Worked from the cell, four formula units in 597.2 ų give 3.945, which reproduces the printed figure to 0.4%. A 20.00 g piece reads 14.85 g in water, on the method at how to measure specific gravity at home.
Antlerite or brochantite? The copper-per-sulfur count
One division settles it. Antlerite is Cu3(SO4)(OH)4 and brochantite Cu4(SO4)(OH)6: both are copper, sulfate and hydroxyl, and the difference is the number of coppers for each sulfur, 3 against 4. Dividing each printed oxide weight by its formula weight, the antlerite sheet’s Chuquicamata analysis (SO3 22.32, CuO 66.34, H2O 10.52, insoluble 0.88) gives 2.991 Cu per S, and the brochantite sheet’s Collahuasi analysis (SO3 17.54, CuO 70.29, H2O 11.96) gives 4.033. Hydrogen comes out at 4.19 and 6.06 per sulfur against the formulas’ 4 and 6.
Documented failure: everything a collector can test by hand. The two sheets print the same three colours, emerald-green, blackish green and pale green, the same pale green streak and a vitreous lustre. Hardness 3.5 sits inside brochantite’s 3.5–4. Densities of 3.88 and 3.97 make a 20.00 g piece read 14.85 g and 14.96 g in water, 0.12 g apart, which matrix or a few per cent of the other mineral would erase. The live brochantite page reaches the same conclusion for antlerite: a sulfate too, which needs analysis rather than a bench test. The optic sign differs, biaxial (+) with 2V 53° against biaxial (–) with 2V 77°, but that needs a polarising microscope and an oriented grain.
A second failure, on the brochantite side. The same cell arithmetic that reproduces antlerite gives 3.981 for brochantite’s printed cell, against its printed 4.09. The figure is reported, not corrected; the measured 3.97 is used here.
Where does antlerite form, and is it a copper ore?
In acid, dry oxidized zones, by its sheet. The Occurrence field reads: “Uncommon, typically formed in the oxidized zone of copper deposits under highly acid conditions, especially in arid regions.” The brochantite sheet is its mirror: “Common in the oxidized zone of copper deposits, yet rarely an ore; formed under low acidity, principally in arid regions.” Antlerite’s associates are brochantite, atacamite, chalcanthite, kröhnkite, natrochalcite, linarite and gypsum; the azurite sheet in turn lists antlerite among azurite’s associates.
Ore at one locality, on the sheet’s wording. The Distribution field calls it “an important copper ore at Chuquicamata, Antofagasta”, Chile. No other locality on the sheet carries that word, and this page does not extend it. How a sheet’s associates and occurrence lines can be read as a sequence is the subject of what is mineral paragenesis.
Where is antlerite found? The sheet’s locality list
Distribution, as printed. In the USA, in Arizona: the Antler mine, near Yucca Station, Mohave Co.; large crystals at several mines in Bisbee, Cochise Co.; the Grandview mine, Grand Canyon, Coconino Co.; Copper Basin, between Skull Valley and Prescott, and Jerome, Yavapai Co. The Blanchard mine, near Bingham, Hansonburg district, Socorro Co., New Mexico; the Darwin district, Inyo Co., California; the Northern Light mine, near Black Mountain, Mineral Co., and other minor occurrences in Nevada; Kennicott, Alaska. Puerto de Gomez, Chihuahua, Mexico. Chuquicamata, Antofagasta, and Remolinos, Atacama, Chile. Ober-Planitz, near Zwickau, Saxony, Germany. Caldbeck Fells, Cumbria, and several mines in Cornwall, England. Capdella, Lerida, Spain. The sheet adds that a number of additional poorly characterized localities are known.
Name, not type locality. The name is for the Antler mine, Arizona, where the first specimens were collected; type material is at the NMNH, 47698. The sheet marks no type locality and the IMA list gives the USA; the term is explained at what is a type locality.
Antlerite and chalcophyllite. The two names are searched together. Neither sheet lists the other as an associate; chalcophyllite is a copper aluminium arsenate-sulfate, Cu18Al2(AsO4)4(SO4)3(OH)24·36H2O on the IMA list, so it shares only the sulfate. More sulfates are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route. Questions about copper compounds and health are routed to toxic minerals in a collection; nothing here is health or safety advice.