Hopeite
Hopeite, Zn3(PO4)2(H2O)4: orthorhombic colourless to pale yellow zinc phosphate, hardness 3.5, density 3.05 to 3.065, white streak, dimorphous with parahopeite.
Hopeite is hydrated zinc phosphate, Zn3(PO4)2(H2O)4 on the IMA list (G, 1826, Belgium): orthorhombic colourless to pale yellow crystals to 6 mm, hardness 3.5, density 3.05 to 3.065, white streak. Parahopeite has the identical IMA formula but is triclinic and denser at 3.31. The Handbook records no green hopeite: its colours stop at pale yellow.
In short
- The dimorph check. A script over the September 2026 IMA-CNMNC Master List returns the same formula for hopeite and parahopeite, Zn3(PO4)2(H2O)4, and both Handbook of Mineralogy sheets say dimorphous. The difference is the structure: orthorhombic Pnma for hopeite, triclinic P1̄ for parahopeite (the bar is lost in the sheet’s text layer and was read from the rendered page).
- The cell check, worked. From the sheet’s cell, a = 10.597, b = 18.318, c = 5.031 Å, Z = 4, hopeite’s density works out to 3.116, the printed figure. Parahopeite’s cell gives 3.319 against its printed 3.32. It packs one formula unit into 229.2 ų against hopeite’s 244.2, and a 20.00 g piece reads 13.96 g in water against 13.44 to 13.47 g.
- Documented failure: “green hopeite”. The hopeite sheet’s colours are colourless, greyish white and pale yellow. Of six zinc phosphates whose sheets all name Kabwe, four print green: phosphophyllite (sea-green), spencerite (pale green), tarbuttite (may be green) and scholzite (rarely lime-green). Three of those read within 0.20 g of hopeite in water, so heft does not sort them.
- The zinc-phosphate ladder. Five IMA rows hold only zinc, phosphorus, oxygen and hydrogen. Tarbuttite and spencerite carry 2 zinc per phosphorus; hopeite, parahopeite and liversidgeite carry 1.5. Worked as oxides, their water runs from 3.71% in tarbuttite to 15.73% in hopeite.
- Where. The Distribution field names Vieille Montagne (Altenberg), Moresnet district, Belgium; Bad Ems, Hagendorf and Oberschulenberg, Germany; large crystals at Kabwe (Broken Hill), Zambia; the Hudson Bay mine near Salmo, British Columbia; and the Tip Top mine, South Dakota, the Palermo #1 mine, New Hampshire, and the Iron Cap mine, Arizona.
| Species | Formula (IMA) | System | Colour on the sheet | Green printed? | Hardness | Density (meas.) | 20.00 g in water | Optic sign |
|---|---|---|---|---|---|---|---|---|
| Hopeite | Zn3(PO4)2(H2O)4 | Orthorhombic | Colourless, greyish white, pale yellow | No | 3.5 | 3.05 to 3.065 | 13.44 to 13.47 g | Biaxial (−) |
| Parahopeite | Zn3(PO4)2(H2O)4 | Triclinic | Colourless, yellow-brown, golden brown | No | 3.5 to 4 | 3.31 | 13.96 g | Biaxial (+) |
| Phosphophyllite | Zn2Fe2+(PO4)2(H2O)4 | Monoclinic | Pale bluish green, sea-green, colourless | Yes | 3 to 3.5 | 3.08 to 3.13 | 13.51 to 13.61 g | Biaxial (−) |
| Spencerite | Zn4(PO4)2(OH)2(H2O)2·H2O | Monoclinic, pseudo-orthorhombic | White, pale green | Yes | About 3 | 3.123 to 3.145 | 13.60 to 13.64 g | Biaxial (−) |
| Scholzite | CaZn2(PO4)2(H2O)2 | Orthorhombic | Colourless to white, pale grey; rarely lime-green, reddish brown, yellow | Rarely | 3 to 4 | 3.11 to 3.13 | 13.57 to 13.61 g | Biaxial (+) |
| Tarbuttite | Zn2(PO4)(OH) | Triclinic, pseudocubic | Colourless, pale yellow, may be brown, red or green | May be | 3.5 to 4 | 4.19 | 15.23 g | Biaxial (−) |
What is hopeite? A hydrated zinc phosphate
Hopeite is Zn3(PO4)2(H2O)4 on the September 2026 IMA list, status G (grandfathered), 1826, country Belgium. The first reference is Transactions of the Royal Society of Edinburgh 10 (1826), 107. The Handbook of Mineralogy hopeite sheet writes the same formula as Zn3(PO4)2·4H2O and names it for Thomas Charles Hope (1766–1844), Professor of Chemistry at the University of Edinburgh.
On the sheet. Orthorhombic, point group 2/m 2/m 2/m, space group Pnma. Crystals are prismatic along [001] or tabular on {010}, to 6 mm, in divergent aggregates or crusts, or compact reniform. Cleavage is perfect on {010}, good on {100} and poor on {001}; fracture uneven; brittle. Hardness 3.5; density 3.05 to 3.065 measured and 3.116 calculated. Colourless, greyish white or pale yellow, white streak, vitreous and pearly on {010}. Biaxial (−), with sections parallel to {100} optically sectorially zoned.
Its chemistry, worked. On standard atomic weights the formula is 42.81% zinc by mass, or ZnO 53.29%, P2O5 30.98% and H2O 15.73%. That reproduces the sheet’s ideal column exactly, which is the arithmetic’s positive control. The Kabwe analysis, ZnO 52.1, P2O5 31.8, H2O 16.1, works out to 2.86 zinc and 3.99 water per two phosphorus.
What is the structure of hopeite? The cell check
One cell, four formula units. The sheet gives an orthorhombic cell a = 10.597(3), b = 18.318(8), c = 5.031(1) Å with Z = 4, and cites Hill and Jones (1976) for the crystal structure. The cell volume is 976.6 ų. Density is Z times the formula mass, 458.14, times 1.66054, divided by the volume: 3.116, exactly the sheet’s calculated figure. The measured 3.05 to 3.065 is 1.6% to 2.1% lower.
The same check on parahopeite. Parahopeite’s triclinic cell, a = 5.768, b = 7.550, c = 5.276 Å, α 93°25′, β 91°11′, γ 91°22′, Z = 1, has a volume of 229.2 ų. The same formula mass gives 3.319 against the printed [3.32]. Hopeite gives each formula unit 244.2 ų, 6.5% more room, which is why the two densities differ while the formula does not.
What that means in the hand. Parahopeite’s measured 3.31 is 8.0% to 8.5% above hopeite’s 3.05 to 3.065. A 20.00 g piece reads 13.96 g in water as parahopeite and 13.44 to 13.47 g as hopeite, a gap of 0.48 to 0.52 g; the method is on how to measure specific gravity at home. The optics agree with the split: hopeite is biaxial negative, parahopeite biaxial positive.
Is there green hopeite? The green-label check
Not on the Handbook sheet. Its colour line reads colourless, grayish white, pale yellow; colorless in transmitted light. A green zinc phosphate on a hopeite label is therefore a question, not an answer. The table above sets hopeite beside the five other zinc phosphates whose sheets all name Kabwe, where the hopeite sheet records large crystals.
Four print green. phosphophyllite is pale bluish green or sea-green; spencerite white or pale green; tarbuttite may be green; scholzite rarely lime-green. Parahopeite, like hopeite, prints no green.
Why heft fails. Phosphophyllite reads 13.51 to 13.61 g, scholzite 13.57 to 13.61 g and spencerite 13.60 to 13.64 g for a 20.00 g piece, all within 0.03 to 0.20 g of hopeite. Only tarbuttite, at 15.23 g, stands clear. What separates the rest is composition: iron in phosphophyllite, calcium in scholzite, hydroxyl in spencerite. That takes an analysis, not a balance.
Where is hopeite found, and how does it relate to the other zinc phosphates?
The Distribution field names nine places. Vieille Montagne (Altenberg), Moresnet district, Belgium; in Germany, Bad Ems, Rhineland-Palatinate, Hagendorf, Bavaria, and Oberschulenberg, Harz Mountains; large crystals at Kabwe (Broken Hill), Zambia; the Hudson Bay mine, about eight km southeast of Salmo, British Columbia; and in the USA the Tip Top mine near Custer, South Dakota, the Palermo #1 mine near North Groton, New Hampshire, and the Iron Cap Pb–Zn mine near Aravaipa, Arizona. Its occurrence line describes a late-stage mineral in some hydrothermal zinc deposits and complex granite pegmatites, also incrusting bone breccia in a limestone cave. It prints no type locality; see what is a type locality.
Associates. At Kabwe: tarbuttite, hemimorphite, spencerite, smithsonite and vanadinite. At the Tip Top mine: triphylite, ferrisicklerite, leucophosphite, laueite, robertsite, hydroxylapatite and sphalerite.
The zinc-phosphate ladder. A script over the IMA list finds 5 rows whose formula holds only zinc, phosphorus, oxygen and hydrogen: tarbuttite Zn2(PO4)(OH) and spencerite Zn4(PO4)2(OH)2(H2O)2·H2O at 2 zinc per phosphorus; hopeite, parahopeite and liversidgeite Zn6(PO4)4(H2O)5·2H2O, IMA 2008-048, at 1.5. Worked as oxides, water is 3.71% in tarbuttite, 13.36% in spencerite, 14.04% in liversidgeite and 15.73% in hopeite and parahopeite. Phosphophyllite shares three of hopeite’s localities: Hagendorf, Palermo #1 and Kabwe. 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.