Hydrozincite
Hydrozincite, Zn5(CO3)2(OH)6, is a white zinc carbonate of oxidised zinc ores: hardness 2 to 2.5, density 4.00, 59.55% zinc, fluorescing pale blue to lilac.
Hydrozincite is a zinc carbonate hydroxide, Zn5(CO3)2(OH)6, hardness 2 to 2.5, density 4.00: soft white, chalky or fibrous crusts from the oxidised zones of zinc deposits, with smithsonite and hemimorphite among its associates. It is 59.55% zinc by mass, and its Handbook sheet says it fluoresces pale blue to lilac under UV.
In short
- What it is. The Handbook of Mineralogy sheet gives Zn5(CO3)2(OH)6, monoclinic, hardness 2 to 2.5, density 4.00, usually as fibrous, stalactitic, reniform or chalky crusts, rarely as bladed crystals to 6 mm. The IMA-CNMNC Master List has the same formula, status G, 1853, Austria.
- The zinc-carbonate ladder. By script, 18 rows of the September 2026 IMA list contain both zinc and carbonate, and 5 contain nothing but Zn, C, O and H. Worked on standard atomic weights, they climb from smithsonite at 52.14% zinc through parádsasvárite 58.17%, hydrozincite 59.55% and brianyoungite 60.50% to sclarite 61.21%.
- Where it sits on the specimen. The sheet says it forms in the oxidised parts of zinc deposits at the expense of sphalerite or smithsonite, with smithsonite, hemimorphite, willemite, cerussite, aurichalcite and calcite as associates, and as crusts in mine workings and caves.
- Documented failure. Weight does not separate it from aurichalcite: a 20.00 g piece reads 15.00 g in water as hydrozincite and 14.95 g as aurichalcite. Colour does, on the sheets: aurichalcite is pale green to sky-blue, hydrozincite colourless to white. Smithsonite reads 15.49 g and is harder, 4 to 4.5.
- Under UV. The sheet: fluoresces pale blue to lilac under UV, with no band named. A second source and the band question are on is hydrozincite fluorescent.
| Mineral | IMA formula | IMA status, year | Zn by mass | Carbonate : metal | Hardness (sheet) | Density, measured (sheet) | 20.00 g piece in water |
|---|---|---|---|---|---|---|---|
| Smithsonite | Zn(CO3) | G, 1832 | 52.14% | 1 : 1 | 4 to 4.5 | 4.43 | 15.49 g |
| Parádsasvárite | Zn2(CO3)(OH)2 | A, 2012-077 | 58.17% | 1 : 2 | Sheet not read | Sheet not read | - |
| Hydrozincite | Zn5(CO3)2(OH)6 | G, 1853 | 59.55% | 2 : 5 | 2 to 2.5 | 4.00 | 15.00 g |
| Brianyoungite | Zn3(CO3)(OH)4 | A, 1991-053 | 60.50% | 1 : 3 | Sheet not read | Sheet not read | - |
| Sclarite | Zn7(CO3)2(OH)10 | A, 1988-026 | 61.21% | 2 : 7 | Sheet not read | Sheet not read | - |
| Aurichalcite (with Cu) | (Zn,Cu)5(CO3)2(OH)6 | G, 1839 | Varies with Cu | 2 : 5 | 1 to 2 | 3.96 | 14.95 g |
| Rosasite (with Cu) | CuZn(CO3)(OH)2 | G, 1908 | Not worked | 1 : 2 | Not read here | Not read here | - |
What is hydrozincite? The sheet’s description
Hydrozincite is a soft zinc carbonate hydroxide, Zn5(CO3)2(OH)6, that usually forms white crusts rather than crystals. The Handbook of Mineralogy hydrozincite sheet gives a monoclinic mineral, point group 2/m, that uncommonly makes lathlike or bladed crystals, flattened on {100} and elongated along [001], with pointed terminations, to 6 mm; much more often it is fibrous, stalactitic, reniform, pisolitic, in isolated spheroids, earthy, chalky or massive. It twins by contact on {100}, cleaves perfectly on {100} and is very brittle. Hardness is 2 to 2.5 and measured density 4.00, calculated 4.01.
Colour and lustre. Colourless, white, grey and pale shades of yellow, brown, pink or green; spherules may be concentrically colour banded. The lustre is pearly, or silky to dull and earthy in aggregates. It is biaxial negative, α 1.635 to 1.640, β 1.736, γ 1.740 to 1.750, with strong dispersion.
Composition, checked. Worked from the formula, hydrozincite is ZnO 74.12%, CO2 16.03% and H2O 9.85%, exactly the sheet’s ideal column; the Goodsprings, Nevada analysis prints ZnO 74.67%, which is 59.99% zinc against 59.55% ideal. The name is for its non-carbonate essential components, water and zinc.
How much zinc is in hydrozincite? The zinc-carbonate ladder
59.55% by mass: more than smithsonite’s 52.14%, less than brianyoungite’s 60.50% or sclarite’s 61.21%. Method: a script parses every row of the September 2026 IMA-CNMNC Master List, rejoining wrapped formulas, and keeps those containing both Zn and CO3. It finds 18; a plain line-by-line scan for the two tokens also finds 18. Five of them contain no element besides zinc, carbon, oxygen and hydrogen, and those five make the ladder tabled above.
What the ladder shows. The more hydroxide a zinc carbonate carries per carbonate, the higher its zinc fraction, because OH weighs less than CO3. Hydrozincite has two carbonates per five zinc. aurichalcite, (Zn,Cu)5(CO3)2(OH)6 on the IMA list, has the same proportions with copper sharing the metal site, so its zinc figure depends on the specimen and is not worked here.
Documented failure. On the sheets read for this page, hydrozincite (D 4.00) and aurichalcite (D 3.96) are 0.05 g apart in water for a 20.00 g piece, closer than a kitchen scale can resolve; their hardness ranges, 2 to 2.5 and 1 to 2, meet. The colour lines separate them: aurichalcite pale green, greenish blue, sky-blue; hydrozincite colourless to white or pale tints. The other three ladder minerals were not read on sheets for this page, so no weights are given for them.
Telling hydrozincite from smithsonite and hemimorphite
Hardness first: hydrozincite is 2 to 2.5, against 4 to 4.5 for smithsonite and 4.5 to 5 for hemimorphite. All three can be white botryoidal crusts on the same oxidised zinc specimen. The smithsonite sheet gives density 4.43, a 20.00 g piece reading 15.49 g in water; hydrozincite reads 15.00 g. The density-first test for the other pair is on smithsonite vs hemimorphite and is not repeated here.
How it forms on them. The hydrozincite sheet says it forms at the expense of sphalerite or smithsonite in the oxidised portions of zinc-bearing deposits, and as incrustations in mine workings and caves, so a soft chalky skin on smithsonite may be a later mineral rather than a coating of dirt. Its associates on the sheet are smithsonite, hemimorphite, willemite, cerussite, aurichalcite, calcite and limonite; hemimorphite, willemite and cerussite have their own pages.
Under a lamp. The sheet says hydrozincite fluoresces pale blue to lilac under UV. Hemimorphite and smithsonite may fluoresce in similar colours, so the glow does not identify it; the comparison and a second source are on is hydrozincite fluorescent.
Where hydrozincite is found: the sheet’s localities
The sheet calls it widespread and names a few localities affording good specimens. Bleiberg, Carinthia, Austria. Monte Malfidano near Buggerru and the Gutturu Pala mine north of Iglesias, Sardinia. In commercial amounts at Picos de Europa near Santander and at Udias, Cantabria, Spain. In the USA, Friedensville, Pennsylvania; Linden, Wisconsin; Joplin, Missouri; around Galena, Kansas; abundant at Goodsprings, Nevada; the Tintic district, Utah; pure masses in the Texas-Arizona mine, Cochise Co., Arizona; Island Ford Cave, Virginia. Fine crystals from the Ojuela mine, Mapimí, Durango, Mexico (see Ojuela). In Iran, the Tchah Kuh, Dareh-Bandjir and Mehdi-Abad mines. In Australia, Paddy’s River mine, the Billy Springs mine in the Flinders Ranges, and Broken Hill, New South Wales. The Shopov cave system, Bulgaria.
What the sheet does not say. It prints no type locality line; the IMA list gives Austria as the country, 1853. Zinc-mineral pages on this site, including rosasite and calcite, are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.