Papagoite vs ajoite
Papagoite is cerulean blue, monoclinic, density 3.25, with calcium; ajoite bluish green, triclinic, 2.96, with potassium. A crystal in quartz needs an analysis.
Papagoite is cerulean blue CaCuAlSi2O6(OH)3, monoclinic, density 3.25; ajoite is bluish-green K3Cu20Al3Si29O76(OH)16·8H2O, triclinic, density 2.96. Calcium says papagoite, potassium says ajoite: papagoite’s formula is 16.80% CaO, ajoite’s has no calcium. Both are recorded with quartz at Messina, and inside a quartz crystal only an analysis tells them apart.
In short
- Criteria first. What decides it depends on what you have. A loose, clean piece: weigh it (13.85 g against 13.24 g in water for 20.00 g) or take its optic sign. A polished face: refractive indices. An inclusion inside quartz: an analysis, because every other measurement reads the host.
- The calcium–potassium rule. Papagoite has one calcium per copper; its formula is 16.80% CaO and the Ajo analysis on its Handbook of Mineralogy sheet 17.02%. Ajoite has 3 potassium per 20 copper and no calcium: Chao, American Mineralogist 66, 201 (1981) found K2O 2.50% and CaO 0.04%. Between these two, calcium points to papagoite and potassium to ajoite.
- Documented failure: the potassium nobody reported. Schaller and Vlisidis, American Mineralogist 43, 1107 (1958) gave an analysis of ajoite with no K2O in it and 0.99% CaO, of which 0.65 was deducted as conichalcite. Chao measured K2O 2.50% by flame photometry; the IMA formula now puts potassium in. An old analysis can miss the element the rule depends on.
- More copper, less weight. From the IMA formulas, ajoite has 0.69 copper per silicon and papagoite 0.50; by mass, 32.46% against 19.04% copper. Yet ajoite is the lighter, 2.96 against 3.25, so weight is no guide to copper content. Its 40.63% CuO agrees with is ajoite a quartz.
- Who each test is wrong for. Colour fails everyone: papagoite’s deep greenish blue and ajoite’s bluish green overlap in the sources’ own words. Weight fails anyone with an inclusion. The calcium–potassium rule fails anyone without an analysis. Nothing here is offered for sale; the wanted list is the only commercial route.
| Reading | Papagoite | Ajoite | Does it separate them? |
|---|---|---|---|
| IMA formula and status | CaCuAlSi2O6(OH)3; A, 1962 s.p., USA | K3Cu2+20Al3Si29O76(OH)16·8H2O; A, 1958, USA | Yes, by analysis |
| CaO, wt% | 16.80 (formula); 17.02 (Ajo analysis) | 0 (formula); 0.04 (Chao); 0.99 in 1958, 0.34 after deducting conichalcite | Yes: calcium means papagoite |
| K2O, wt% | 0 (formula); no K2O in the Ajo analysis | 3.61 (formula); 2.50 (Chao); not reported in 1958 | Yes: potassium means ajoite |
| Cu per Si | 0.50 (formula); 0.529 (Ajo analysis) | 0.69 (formula); 0.774 (Chao, 6.97 per 9 Si) | Yes, with an analysis |
| Cu by mass; CuO | 19.04%; 23.83% (formula), 23.53% (analysis) | 32.46%; 40.63% (formula), 42.2% (Chao), 33.90% (1958) | Yes, with an analysis |
| System | Monoclinic, C2/m | Triclinic (Chao; Pluth and Smith) | Yes, by X-ray |
| Habit | Equant crystals to 3 mm; radiating aggregates enclosed in quartz; massive veneers | Laths flattened on {010}, averaging 0.01 × 0.1 × 0.4 mm (Chao); plates a millimetre and less (1958); mostly compact massive | Sometimes, under magnification |
| Hardness | 5 to 5.5 | Not printed in the fetched sources | Not quotable |
| Density | 3.25 measured and calc. | 2.96 (1958, pycnometer); 2.951 calc. (1981) | Yes, on a clean piece |
| 20.00 g in water | 13.85 g | 13.24 g | Yes, about 0.6 g; not for an inclusion |
| Optic sign | Biaxial (−) | Biaxial (+) | Yes, with a microscope |
| Refractive indices | α 1.607, β 1.641, γ 1.672 | α 1.550 to 1.565, β 1.583 to 1.590, γ 1.641 to 1.650 | Yes, on a polished face |
| Birefringence, worked | 0.065 | 0.085 (1958); 0.091 (1981) | Yes |
| Pleochroism | X colourless to very pale greenish blue; Y blue; Z deep greenish blue | X very light bluish green; Y = Z brilliant bluish green (1981) | Weakly |
| Colour | Cerulean blue | Bluish green; about 75% green, 25% blue (1958) | No: the words overlap |
| Localities as printed | New Cornelia mine, Ajo; Messina; Sinclair mine, Lüderitz (sheet) | Ajo, Pima County, Arizona (1958); New Cornelia mine (1981); with papagoite at Messina (papagoite sheet) | No: they share two |
Which test tells papagoite from ajoite? The criteria
Choose by what you are holding, not by colour. Papagoite and ajoite are both copper aluminium silicates with hydroxyl, both from Ajo, Arizona, and both recorded with quartz at Messina, South Africa, by the papagoite sheet. Their colour descriptions run into each other. What does separate them, in order of how little it needs:
1. A loose, clean piece: weigh it. Worked as 20 − 20/D, 20.00 g reads 13.85 g in water as papagoite (3.25) and 13.24 g as ajoite (2.96), about 0.6 g apart; the method is on how to measure specific gravity at home. 2. A grain under a polarising microscope: the optic sign. Papagoite is biaxial negative on its sheet; ajoite biaxial positive in both Schaller and Vlisidis (1958) and Chao (1981). 3. A polished face: the indices. Ajoite’s α, 1.550 to 1.565, and β, 1.583 to 1.590, sit below papagoite’s α 1.607 and β 1.641; its γ, 1.641 to 1.650, overlaps papagoite’s β, so read more than one index. 4. An inclusion inside quartz: an analysis. The weight and indices of such a piece are quartz’s, as is ajoite a quartz explains.
Papagoite or ajoite by analysis: the calcium–potassium rule
Between the two, calcium means papagoite and potassium means ajoite. On the September 2026 IMA-CNMNC Master List, papagoite is CaCuAlSi2O6(OH)3, one calcium for each copper, and ajoite K3Cu2+20Al3Si29O76(OH)16·8H2O, with potassium and no calcium. Worked on standard atomic weights, papagoite is 16.80% CaO and ajoite 3.61% K2O. The analyses agree: the Handbook papagoite sheet prints 17.02% CaO and no potassium for Ajo; Chao’s ajoite gives CaO 0.04%, K2O 2.50% and Na2O 0.84%, which recast to 0.70 K, 0.36 Na and 0.01 Ca per 9 silicon. Pluth and Smith, PNAS 99, 11002 (2002), abstract names K and Na as major substituents in their microprobe analysis.
The documented failure. Schaller and Vlisidis, American Mineralogist 43, 1107 (1958) published the first ajoite analysis with no K2O line. It shows 0.99% CaO, of which 0.65 was deducted with 3 per cent of admixed conichalcite, leaving 0.34. Their spectrographic list does not mention potassium either way. Chao, analysing Na2O and K2O by flame photometry on hand-picked material, found 2.50% K2O. A reader applying the rule to the 1958 figures alone would find no potassium and a little calcium, the opposite of the answer. The rule needs a modern analysis, or at least one that looked for potassium.
Which has more copper, papagoite or ajoite?
Ajoite, by any measure, and it is still the lighter mineral. From the IMA formulas, ajoite has 20 copper to 29 silicon, 0.69, and papagoite 1 to 2, 0.50. By mass that is 32.46% copper against 19.04%, or CuO 40.63% against 23.83%. Chao’s ajoite analysis is richer still, 42.2% CuO and 6.97 copper per 9 silicon, 0.774. The 1958 analysis gave 33.90%, its silica carrying quartz, as is ajoite a quartz sets out.
Why that is not a test in the hand. Ajoite’s density, 2.96, is below papagoite’s 3.25 despite the extra copper. So weight sorts the two minerals, but not by copper content, and this page does not offer a reason for the difference. The copper ratios of the copper-only silicates are a different ladder, on the shattuckite page, and the chrysocolla question is on shattuckite vs chrysocolla.
Papagoite and ajoite in quartz: what Messina records
The papagoite sheet is the source, and it names both. It records papagoite as sheets and rings of microcrystalline radiating aggregates enclosed in quartz crystals, gives its occurrence as included in quartz crystals at Messina, South Africa, and lists quartz and ajoite as its associates there. At Ajo it lists aurichalcite, shattuckite, ajoite and barite. No source fetched for this page describes the Messina ajoite itself, so this page does not say how the inclusions look or which is commoner.
Who each test is wrong for. Colour is wrong for everyone: papagoite’s pleochroism runs to deep greenish blue and ajoite’s to brilliant bluish green, so a blue inclusion can be either. Weight and refractive index are wrong for anyone holding an inclusion, because the quartz host is what is measured; how such zones are read is on what is a phantom crystal. The calcium–potassium rule is wrong for anyone without an analysis. A label naming one of the two on an included crystal is a claim to ask the basis of. The species are on papagoite and is ajoite a quartz; more guides are in the collecting guides.
Are papagoite and ajoite a hazard?
This page does not assess it. Both are copper silicates; hazard questions about copper minerals go to toxic minerals in a collection, and to HSE or a clinician for anything specific. This is not health or safety advice.