Lazulite
Lazulite, MgAl2(PO4)2(OH)2: the magnesium end of the series with scorzalite. Hardness 5.5 to 6, density 3.122 to 3.240, azure-blue to yellow-green, pleochroic.
Lazulite is a magnesium aluminium phosphate, MgAl2(PO4)2(OH)2 on the IMA list (A, 1967 s.p., Austria), the magnesium end of a series with iron-rich scorzalite. It is monoclinic, hardness 5.5 to 6, density 3.122 to 3.240, azure-blue to sky-blue, but its sheet also lists yellow-green and green, with strong colourless-to-blue pleochroism.
In short
- One mineral, one end of a series. The September 2026 IMA-CNMNC Master List writes MgAl2(PO4)2(OH)2, status A, 1967 s.p., country Austria, and the Handbook of Mineralogy sheet writes the same and says it forms a series with scorzalite. In Pecora and Fahey, American Mineralogist 35 (1950) the name scorzalite applies only where the Fe:Mg molecular ratio exceeds 50:50; below that the mineral is lazulite. Where the line falls in practice is worked on lazulite vs scorzalite.
- The 3.144 check. The sheet’s cell (a 7.144, b 7.278, c 7.228 Å, β 120.50°, Z = 2) has a volume of 323.81 ų. The pure magnesium formula, 302.22 g/mol, gives 3.100 on it, 0.044 below the printed D(calc.) 3.144. The printed figure is reached at about Mg0.86Fe0.14. The sheet does not say which composition it used, so this is a reading of its arithmetic, not an analysis.
- Not always blue. The sheet lists azure-blue, sky-blue, bluish white, yellow-green, blue-green and rarely green. Pecora and Fahey describe green lazulite from Stoddard, New Hampshire, with blue admixed, and found no definite correlation of colour with composition. Pleochroism is the constant: strong, X colourless, Y blue, Z darker blue.
- Documented failure: measured lighter than the arithmetic. The sheet’s analysis (1), Graves Mountain, Georgia, is oxide for oxide Pecora and Fahey’s sample 2 (Mg:Fe 82:18), and its measured 3.122 is the sheet’s lower bound. On the sheet’s cell that composition works out at 3.158; their Dattas, Brazil, sample (88:12) measured 3.118 against 3.138 worked. A 20.00 g piece reads 13.59 g in water either way, so the balance does not read iron content inside the lazulite range.
- Where. The sheet names Färbergraben and Höllgraben near Werfen, Austria; Hålsjöberg in Värmland, Sweden, for very large crystals; Graves Mountain, Georgia; Cross-cut Creek in the Big Fish River–Rapid Creek area, Yukon; near Dattas, Minas Gerais; Mt. Bity, Madagascar; and fine gemmy crystals from the Chilas area near Nanga Parbat, Pakistan. It marks no type locality.
| Composition | Fe2+ per formula unit | Formula mass | Worked on the lazulite cell | Printed or measured | 20.00 g in water, at the printed or measured figure |
|---|---|---|---|---|---|
| Pure MgAl2(PO4)2(OH)2 | 0 | 302.22 | 3.100 | — | 13.55 g (worked figure) |
| What the printed figure needs | 0.137 | 306.55 | 3.144 | D(calc.) 3.144 (sheet) | 13.64 g |
| Dattas, Minas Gerais (Pecora and Fahey no. 1, Mg:Fe 88:12) | 0.12 | 306.00 | 3.138 | SG 3.118 (measured) | 13.59 g |
| Graves Mountain, Georgia (sheet analysis (1); Pecora and Fahey no. 2, 82:18) | 0.18 | 307.90 | 3.158 | SG 3.122 (measured; the sheet’s lower bound) | 13.59 g |
| Upper end of the sheet’s measured range | — | — | — | D(meas.) 3.240 (sheet) | 13.83 g |
| Fe:Mg = 1:1 (the sheet’s column (2)) | 0.50 | 317.99 | 3.261 | Not a measurement | — |
What is lazulite? The formula and the series with scorzalite
A magnesium aluminium phosphate. The September 2026 IMA list gives MgAl2(PO4)2(OH)2, status A, 1967 s.p., country Austria, with a first reference of 1795 and a second in Physics and Chemistry of Minerals 46 (2019). The Handbook of Mineralogy lazulite sheet writes the same formula and puts it in the lazulite group. On standard atomic weights the formula mass is 302.22 and the mineral is 8.04% magnesium; the ideal oxide column, MgO 13.34, Al2O3 33.74, P2O5 46.97, H2O 5.96, matches the end-member column Pecora and Fahey printed in 1950 to within 0.01.
Where the name stops. The sheet says lazulite forms a series with scorzalite, the Fe2+ member. Pecora and Fahey’s 1950 paper on the series applies the name scorzalite only to members whose Fe:Mg molecular ratio exceeds 50:50, and, following Schaller (1930), accepts ferroan lazulite and magnesian scorzalite for the intermediate range; they call the Graves Mountain material ferroan lazulite (Mg82:Fe18). An unanalysed blue phosphate from this series cannot be named on sight; the evidence is set out on lazulite vs scorzalite, and the scorzalite end on scorzalite.
What colour is lazulite? Blue to green, and pleochroic
Six colours on the sheet. Azure-blue, sky-blue, bluish white, yellow-green, blue-green and rarely green, with a white streak and vitreous lustre; transparent to translucent, and may be nearly opaque. Pecora and Fahey describe the Stoddard, New Hampshire, lazulite as green with blue lazulite admixed, the light blue of Graves Mountain, Dattas and Clubbs Mountain material, and the dark blue of California specimens, and they found no definite correlation of colour with composition. The streak method is on how to use a streak plate.
What is constant is pleochroism. The sheet prints it as strong: X colourless, Y blue, Z darker blue, with Y parallel to b. So a transparent grain changes from colourless to blue as it is turned in polarised light. Lapis lazuli, which the name suggests, is a rock whose blue mineral is lazurite; how the two are told apart, with its own refractometer rule, is on is lazulite the same as lapis lazuli and is not repeated here.
The 3.144 check, worked
Method. The sheet prints a monoclinic cell, space group P21/c, a 7.144(1), b 7.278(1), c 7.228(1) Å, β 120.50(1)°, Z = 2. Its volume, abc·sin β, is 323.81 ų. Two formula units of pure MgAl2(PO4)2(OH)2 in that volume give a density of 3.100. The sheet prints D(calc.) 3.144. Solving for the formula mass that gives 3.144 on the same cell returns 306.55, which is MgAl2(PO4)2(OH)2 with about 0.137 of its magnesium replaced by ferrous iron.
What it shows, and what it does not. The printed calculated density is not that of the pure magnesium formula; it fits a slightly ferroan lazulite, close to Pecora and Fahey’s Dattas sample at Mg:Fe 88:12. The cell itself grows with iron: scorzalite’s printed cell is 0.74% larger. So the check identifies the arithmetic, not the specimen, and the sheet does not say which crystal its cell or its 3.144 came from.
Documented failure: the measured densities run low. Graves Mountain, whose analysis the sheet prints, works out at 3.158 on this cell, but Pecora and Fahey measured 3.122 on the analysed split with a fused-silica pycnometer. Dattas works out at 3.138 and measured 3.118. Both read 13.59 g in water for 20.00 g, against 13.83 g at the sheet’s top figure, 3.240. Method on how to measure specific gravity at home.
Where is lazulite found?
As the sheet prints it. Many minor localities; well-crystallised or rich material from Färbergraben and Höllgraben, near Werfen, Salzburg, Austria. In Sweden, very large crystals from Hålsjöberg, Värmland, and in the Västanå iron mine, Skåne. In the USA, large crystals from Graves Mountain, Lincoln Co., Georgia; from about 30 km southeast of Beatty, Nye Co., Nevada; at the Champion mine and the nearby Vulcanus claim, White Mountains, Mono Co., California. Fine crystals along Cross-cut Creek, Big Fish River–Rapid Creek area, Yukon Territory, Canada. From 15 km west of Dattas, Minas Gerais, Brazil. On Mt. Bity, Ranomainty, and near Jamalezo, Madagascar. Fine gemmy crystals from the Chilas area, near Nanga Parbat Peak, Pakistan. No type locality is marked; see what is a type locality.
Two settings. In metamorphic rocks the sheet’s associates are quartz, andalusite, rutile, kyanite, corundum, muscovite, pyrophyllite, dumortierite, wagnerite, svanbergite and berlinite; in pegmatites, albite, quartz, muscovite, tourmaline and beryl. Pecora and Fahey add that in granitic pegmatites lazulite or scorzalite occurs in the border zone rather than the central zone. The brazilianite sheet names lazulite-scorzalite among its own associates at Buranga, Rwanda. Other phosphates are in the species index.
Is lazulite a gemstone? What it is used for
Cut, on the record. The sheet prints fine gemmy crystals from the Chilas area. Pecora and Fahey write that lazulite from many localities, particularly with clear quartz, is of such clarity that it has been cut into gem stones, and that Kerr (1926) gave gem lazulite the name berkeyite, which they say can apply to gem scorzalite as well. No fetched source names another use, so this page states none.
Hardness and cleavage. Hardness 5.5 to 6, cleavage poor to good on {110} and indistinct on {101}, fracture uneven to splintery, tenacity brittle. A scratch test on a crystal risks a cleavage break; method on how to test mineral hardness properly and cleavage or fracture: how to tell. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.