Witherite
Witherite is barium carbonate, BaCO3: orthorhombic, aragonite group, hardness 3 to 3.5. A 20.00 g piece reads 15.26 to 15.36 g in water, just under baryte.
Witherite is barium carbonate, BaCO3, an orthorhombic aragonite-group mineral: hardness 3 to 3.5, density 4.22 to 4.31, named for William Withering. A 20.00 g piece reads 15.26 to 15.36 g in water, between strontianite at 14.68 g and baryte at 15.56 g. Its birefringence, 0.148 worked from the sheet, is twelve times baryte’s 0.012.
In short
- The formula and the group. The September 2026 IMA-CNMNC Master List lists witherite as Ba(CO3), status G, 1789, United Kingdom. The Handbook of Mineralogy sheet writes BaCO3, places it in the aragonite group, and says it forms a series with strontianite. Worked: 69.59% barium; the sheet’s Anglezark, England analysis corresponds to (Ba0.99Sr0.01)CO3.
- The aragonite-group ladder. A script over all 416 cached Handbook sheets finds 4 that print Aragonite group: aragonite (Ca), strontianite (Sr), witherite (Ba) and cerussite (Pb). In water a 20.00 g piece reads 13.22 g as aragonite, 14.68 g as strontianite, 15.26 to 15.36 g as witherite and 16.95 g as cerussite: heavier with each heavier cation.
- Witherite or baryte: the birefringence split. Both are white barium minerals of hardness 3 to 3.5. Witherite is biaxial (−) with γ − α = 0.148; baryte is biaxial (+) with 0.012, twelve times less. Baryte’s cleavage is perfect on {001}, witherite’s distinct on {010}. The baryte page’s heavy-spar window is not repeated here.
- Where weight fails, documented. Baryte reads 15.56 g, only 0.20 g above the heaviest witherite. Alstonite and barytocalcite, both BaCa(CO3)2 on the IMA list, read 14.54 to 14.61 g, within 0.07 to 0.15 g of strontianite. And all six carbonate sheets here print some fluorescence, so a UV lamp does not sort them.
- Northern England, as printed. The Distribution field gives Alston Moor, Cumbria, and fine crystals from the Settlingstones mine, near Fourstones, and Fallowfield, near Hexham, Northumberland. The district is on Alston Moor.
| Mineral | Formula (IMA) | Group or system (sheet) | Hardness | Density | 20.00 g piece in water | Birefringence | Luminescence on the sheet |
|---|---|---|---|---|---|---|---|
| Aragonite | Ca(CO3) | Aragonite group | 3.5 to 4 | 2.95 | 13.22 g | 0.155 | Fluorescent red or yellow, LW and SW UV; phosphorescent |
| Strontianite | Sr(CO3) | Aragonite group | 3.5 | 3.76 | 14.68 g | 0.150 | Fluorescent under UV |
| Witherite | Ba(CO3) | Aragonite group | 3 to 3.5 | 4.22 to 4.31 | 15.26 to 15.36 g | 0.148 | Fluorescent and phosphorescent under UV |
| Cerussite | Pb(CO3) | Aragonite group | 3 to 3.5 | 6.55 | 16.95 g | 0.273 | May fluoresce yellow, LW UV |
| Baryte | Ba(SO4) | Barite group | 3 to 3.5 | 4.50 | 15.56 g | 0.012 | May fluoresce and phosphoresce, cream to spectral colours |
| Alstonite | BaCa(CO3)2 | Triclinic, pseudo-orthorhombic | 4 to 4.5 | 3.707 | 14.60 g | 0.146 | Fluoresces yellow, SW and LW UV |
| Barytocalcite | BaCa(CO3)2 | Monoclinic | 3.5 to 4 | 3.66 to 3.71 | 14.54 to 14.61 g | 0.161 | Pale yellowish to red, SW and LW UV |
| Celestine | Sr(SO4) | Orthorhombic | 3 to 3.5 | 3.97 | 14.96 g | Not used | Not used |
What is witherite? Barium carbonate of the aragonite group
Witherite is barium carbonate, BaCO3, a grandfathered species first published in 1789 from the United Kingdom. The September 2026 IMA-CNMNC Master List writes it Ba(CO3), status G, with its first reference in the Bergmannisches Journal of 1789. The Handbook of Mineralogy sheet places it in the aragonite group and says it forms a series with strontianite. On standard atomic weights the formula mass is 197.34: 69.59% barium, or 77.70% BaO and 22.30% CO2, the sheet’s ideal column exactly.
The analysis. The sheet’s electron-microprobe analysis is from Anglezark, England: BaO 77.15, SrO 0.68, CaO 0.08, with CO2 calculated, corresponding to (Ba0.99Sr0.01)CO3. Worked by moles, barium is 98.4% of the large cations. The strontianite it forms a series with is SrCO3; this specimen sits at the barium end.
What the sheet records. Orthorhombic, point group 2/m 2/m 2/m; pseudohexagonal dipyramidal crystals due to repeated twinning, short prismatic to elongated along [001], faces commonly rough and horizontally striated, to 12 cm; also botryoidal to spherical, columnar fibrous, granular and massive. Twinning on {110}, universal. Cleavage distinct on {010}, poor on {110} and {012}. Hardness 3 to 3.5; density 4.22 to 4.31. Biaxial (−), α 1.529, β 1.676, γ 1.677, 2V 16°. Colourless, white or pale grey, sometimes tinted pale yellow, brown or green; streak white; vitreous, resinous on fractures.
The aragonite-group ladder: one structure, four cations
The aragonite-group ladder: on the Handbook sheets the group’s four members get heavier with each heavier cation, calcium to strontium to barium to lead, and witherite is the barium rung. Method: every cached sheet in refcache/hom, 416 of them, converted with pdftotext -layout and searched for Aragonite group; 4 match: aragonite, strontianite, witherite and cerussite. All four are orthorhombic, point group 2/m 2/m 2/m, space group Pmcn, biaxial (−).
Worked, for a 20.00 g piece in water. Aragonite at 2.95 reads 13.22 g; strontianite at 3.76, 14.68 g; witherite at 4.22 to 4.31, 15.26 to 15.36 g; cerussite at 6.55, 16.95 g. The step from strontianite to witherite is 0.58 g. The method is on how to measure specific gravity at home.
What the ladder does not say. It ranks the four sheets that print the group name; it is not a list of the group, and the IMA list prints no group column. A script over the IMA list finds 13 rows with a single cation and the formula M(CO3), among them calcite, aragonite and vaterite, all three Ca(CO3), so formula alone does not place a carbonate in this group.
Witherite or baryte? Birefringence 0.148 against 0.012
The birefringence split: witherite’s γ − α is 0.148, baryte’s 0.012, so under crossed polars or on a refractometer the two barium minerals are not close. Worked from the sheets: witherite α 1.529, γ 1.677, biaxial (−); baryte α 1.636, γ 1.648, biaxial (+). Witherite’s low index, 1.529, is 0.107 below baryte’s lowest.
Cleavage and habit. Baryte has perfect {001} cleavage and is commonly thin to thick tabular; witherite’s best cleavage is distinct on {010}, and its crystals are pseudohexagonal dipyramids from universal {110} twinning. Both are hardness 3 to 3.5 with a white streak. Worked, BaCO3 is 69.59% barium and BaSO4 58.84%, the same baryte figure as the baryte page, whose heavy-spar window is not repeated here.
The balance is weak here, documented. In water a 20.00 g piece of baryte, at 4.50, reads 15.56 g; witherite reads 15.26 to 15.36 g. Baryte is 4.4% to 6.6% denser, a gap of 0.20 g at its narrowest. USGS Open-File Report 99-529, Table 1 left both unpulled at 1.70 amp, witherite on 1 sample and baryte on 6, so a magnet does not help either.
Where the ladder fails: alstonite, barytocalcite and UV
Alstonite and barytocalcite, the barium–calcium carbonates of the same district, fall between strontianite and witherite by weight. The IMA list gives both as BaCa(CO3)2: alstonite G, 1841, and barytocalcite G, 1824, both United Kingdom, with paralstonite, A 1979-015, USA, as the third row of that formula. Their sheets read 3.707 and 3.66 to 3.71: 14.54 to 14.61 g in water, 0.65 g or more under witherite but within 0.15 g of strontianite. Alstonite is triclinic, pseudo-orthorhombic, and hardness 4 to 4.5; barytocalcite is monoclinic with perfect {210} cleavage.
Fluorescence does not sort them. Read ligature-aware, with hemimorphite and willemite as positive controls, all four aragonite-group sheets and both BaCa(CO3)2 sheets print a luminescence line. Witherite’s reads fluorescent and phosphorescent under UV, X-rays, and electron beams, with no colour; this page gives none and no cause. The lamp and the wavelengths are on fluorescent minerals explained.
Habit is the sheet’s own clue. The alstonite sheet describes steep pseudohexagonal dipyramids to 6 mm; the witherite sheet, dipyramids to 12 cm, faces commonly rough and horizontally striated. A label that matters should carry a determination rather than a habit guess.
Where witherite is found: Northern England and beyond
The Distribution field gives only a few localities: in England, Alston Moor, Cumbria, and fine crystals from the Settlingstones mine, near Fourstones, and Fallowfield, near Hexham, Northumberland; Leogang and Peggau, north of Graz, Styria, Austria; Příbram, Czech Republic; Freiberg and St. Andreasberg, Germany; the Arkhyz deposit, Caucasus Mountains, Russia; fine large crystals from mines around Rosiclare, as the Minerva #2 mine, Cave-in-Rock, Hardin Co., Illinois, and Pigeon Roost, Montgomery Co., Arkansas; the Jason Pb–Zn deposits, Macmillan Pass, Yukon; large deposits from Ziyang to Chengkou, on the Shaanxi–Sichuan boundary, China; the Hasei mine, Akita Prefecture, Japan; and the Hunter Valley coal deposits, New South Wales.
How it forms. The Occurrence field: usually in minor amounts in low-temperature hydrothermal veins, typically an alteration product of baryte; possibly of anoxic sedimentary origin with barium from volcanic hot springs; uncommon in coal measures. Its associates are baryte, fluorite, calcite and galena. The North Pennine setting is on Alston Moor and Weardale.
Barium. Hazard questions are outside this page; the site’s routing notes are toxic minerals in a collection and is baryte toxic, and neither is advice. Strontium’s sulphate is on celestine. 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.