Tsumebite
Tsumebite, Pb2Cu(PO4)(SO4)(OH): emerald-green monoclinic lead copper phosphate-sulfate, always twinned, hardness 3.5, density 6.01–6.13, first noted at Tsumeb.
Tsumebite is a lead copper phosphate-sulfate, Pb2Cu(PO4)(SO4)(OH) on the IMA list (G, 1912, Namibia). Its Handbook sheet gives emerald-green monoclinic plates to 3 mm, always twinned, hardness 3.5, density 6.01 to 6.13, and a rare secondary mineral in arsenic-bearing Pb–Cu deposits. Worked, it is 60.41% lead and 9.26% copper.
In short
- Formula and status. The September 2026 IMA-CNMNC Master List gives Pb2Cu(PO4)(SO4)(OH), status G (grandfathered), 1912, Namibia; the Handbook of Mineralogy sheet writes the same and files it in the brackebuschite group. Worked on standard atomic weights: formula mass 685.98, lead 60.41%, copper 9.26%, phosphorus 4.52%, sulfur 4.67%, which reproduces the sheet’s ideal oxide column to the second decimal.
- What it looks like, per the sheet. Emerald-green to bluish green, vitreous and brilliant, transparent; platy monoclinic crystals with large {110} and {101}, to 3 mm, always twinned. Hardness 3.5, brittle, uneven fracture. The sheet prints neither a cleavage nor a streak, and this page supplies neither.
- The phosphorus check. The IMA list also has arsentsumebite, Pb2Cu(AsO4)(SO4)(OH), G, “1935 ?”, Namibia: the same formula with arsenate for phosphate. The sheet’s Tsumeb analysis, PbO 65.09, CuO 11.97, P2O5 10.26, recasts to 0.991 P and 1.032 Cu per 2 Pb, so the analysed material is the phosphate. Ideal arsentsumebite would print no P2O5 and 15.74% As2O5.
- Documented failure: the analysis is incomplete. Its SO3 and H2O are “n.d.” (not determined) and it reports no arsenic, so the three determined oxides total 87.32. The 12.68 missing is close to the ideal SO3 plus H2O of 12.98, but that is consistent, not proven. A second failure: the sheet’s cell gives 6.182, not its printed D(calc.) 6.22.
- Where. The Distribution field names Tsumeb, Namibia; Kipushi, Congo; Morenci and the Mammoth-St. Anthony mine, Arizona; the Mex-Tex mine, New Mexico; the Blue Bell claims, California; the Black Pine mine, Montana; Roughton Gill, Carrock Fell, Cumbria; Altenmittlau and the Clara mine, Germany; and Broken Hill, New South Wales.
| Material | Source | P2O5 | As2O5 | SO3 | PbO / CuO | P per 2 Pb | Density | 20.00 g in water |
|---|---|---|---|---|---|---|---|---|
| Tsumebite, ideal Pb2Cu(PO4)(SO4)(OH) | IMA (G, 1912, Namibia); sheet column (2) | 10.35 | 0 | 11.67 | 65.07 / 11.60 | 1 | 6.22 printed; 6.182 from the cell | 16.78 g (6.22) |
| Tsumeb, Namibia (sheet analysis 1) | Handbook tsumebite sheet | 10.26 | Not reported | n.d. | 65.09 / 11.97 | 0.991 | 6.01–6.13 measured | 16.67–16.74 g |
| Arsentsumebite, ideal Pb2Cu(AsO4)(SO4)(OH) | IMA (G, “1935 ?”, Namibia); worked | 0 | 15.74 | — | 61.16 / 10.90 | 0 | No sheet consulted | — |
| Brackebuschite, Pb2Mn3+(VO4)2(OH) | IMA (G, 1880, Argentina) | — | — | — | — | — | No sheet consulted | — |
| Arsenbrackebuschite, Pb2Fe3+(AsO4)2(OH) | IMA (A, 1977-014) | — | — | — | — | — | No sheet consulted | — |
What is tsumebite? A lead copper phosphate-sulfate
The formula. The September 2026 IMA list gives Pb2Cu(PO4)(SO4)(OH), status G, 1912, with Namibia as the country of first description. The Handbook of Mineralogy tsumebite sheet writes the same formula and puts it in the brackebuschite group. Each formula unit carries two lead atoms, one copper, one phosphate, one sulfate and one hydroxyl. Worked on standard atomic weights, lead is 414.4 of a formula mass of 685.98, 60.41%, and copper 9.26%; the oxides come to PbO 65.07, CuO 11.60, P2O5 10.35, SO3 11.67 and H2O 1.31, the sheet’s column (2) exactly.
What the sheet describes. Monoclinic, point group 2/m, space group P21/m; typically well crystallised and platy, with large {110} and {101}, narrow {100} and many minor forms, to 3 mm. Always twinned on {-122}, may be multiple, with serrated re-entrants oscillatory between {011} and {-104}; the overbars on those two indices were read from the rendered sheet. Uneven fracture, brittle, hardness 3.5. Emerald-green to bluish green, green in transmitted light, vitreous to brilliant, transparent. Optically biaxial (+), α 1.885 to 1.900, β 1.920, γ 1.943 to 1.956, 2V about 90°, with strong dispersion (r less than v) and a faint pleochroism to robin’s-egg-blue along Z. Other lead and copper minerals are in the species index.
Tsumebite or arsentsumebite? The phosphorus check
Why it is asked. The IMA list carries both tsumebite, Pb2Cu(PO4)(SO4)(OH), and arsentsumebite, Pb2Cu(AsO4)(SO4)(OH), status G with the year printed “1935 ?” and Namibia as the country. The sheet’s X-ray pattern, from the Otavi mine, Southwest Africa [=Tsumeb, Namibia], is described as close to arsentsumebite, and its reference list includes a 1994 Lapis article whose title asks, in German, whether a Tsumeb specimen is tsumebite or arsentsumebite. A powder pattern close to another mineral’s does not decide between them; the anion does.
The check, worked. The sheet’s analysis (1), from Tsumeb, prints P2O5 10.26, CuO 11.97 and PbO 65.09. Divided by molar masses and scaled to two lead atoms, that is 0.991 phosphorus and 1.032 copper, against 1 and 1 in the formula. Ideal arsentsumebite would print no P2O5 and 15.74% As2O5. On phosphorus alone, the analysed material is tsumebite.
Documented failure. The same analysis leaves SO3 and H2O as “n.d.” and lists no As2O5, so it cannot show how much arsenic, if any, sits on the phosphate site, and the three oxides it does report total 87.32. The 12.68 shortfall is near the formula’s SO3 plus H2O, 12.98, which is consistent with the sulfate half but does not measure it. A label reading tsumebite on a Tsumeb specimen records the phosphate name; without an analysis it does not exclude arsenate.
How heavy is tsumebite? Density, worked
The numbers. The sheet prints D(meas.) 6.01 to 6.13 and D(calc.) 6.22. A 20.00 g piece therefore reads 16.67 to 16.74 g in water, or 16.78 g at the calculated value; the method is on how to measure specific gravity at home. The sheet records crystals only to 3 mm, so these figures describe the mineral rather than any one crystal.
Documented failure: the cell. The sheet lists a P21/m cell, a 8.70, b 5.80, c 7.85 Å with the angle printed as α = 111.5°, Z = 2. Taking that angle as the monoclinic one, V = abc·sin 111.5° = 368.55 ų, and Z·M·1.66054/V gives 6.182, not the printed 6.22. The sheet does not say which cell or composition its 6.22 uses, and this page does not correct it. The arsenate formula on the same cell would give 6.578, a figure that only shows the mass effect of swapping phosphorus for arsenic; no arsentsumebite sheet was consulted.
Where tsumebite is found
Occurrence. The sheet calls tsumebite a rare secondary mineral in the oxidized zone of some arsenic-bearing Pb–Cu deposits. Associates: azurite, smithsonite, malachite, cerussite, mimetite, wulfenite and olivenite.
Distribution, as printed. From Tsumeb, Namibia; at Kipushi, 28 km southwest of Lubumbashi, Katanga Province, Congo; in Arizona, at Morenci, Greenlee Co., and the Mammoth-St. Anthony mine, Tiger, Pinal Co.; the Mex-Tex mine, near Bingham, Hansonburg district, New Mexico; the Blue Bell claims, near Baker, California; the Black Pine mine, near Philipsburg, Montana; Roughton Gill, Carrock Fell, Cumbria, England (see Caldbeck Fells); Altenmittlau, Hesse, and the Clara mine, near Oberwolfach, Black Forest, Germany; and Broken Hill, New South Wales. The name records its first-noted occurrence at Tsumeb; the sheet marks no type locality and says the type material was destroyed by bombing; see what is a type locality. Duftite, a lead copper arsenate, is named for the general manager of the same mine, per its sheet.
Hazard, in one line. Tsumebite is 60.41% lead and 9.26% copper by formula; any hazard question is routed to toxic minerals in a collection, and this is not advice. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.