Lazulite vs scorzalite
Lazulite and scorzalite are two species of one phosphate series; the name changes where iron passes magnesium. Analysis decides; colour and locality do not.
Lazulite and scorzalite are one series, and the name follows the ratio: scorzalite where Fe:Mg exceeds 50:50, lazulite below (Pecora and Fahey, 1950). Analysis decides. In their eight samples every lazulite read α 1.620 or less and SG 3.190 or less, every scorzalite α 1.633 and SG 3.268 or more. Colour does not separate them.
In short
- Criteria first: the ratio is the definition. The IMA-CNMNC Master List has two rows, lazulite MgAl2(PO4)2(OH)2 and scorzalite Fe2+Al2(PO4)2(OH)2, and both Handbook of Mineralogy sheets say the two form a series. Pecora and Fahey, American Mineralogist 35 (1950) applies the name scorzalite only where the Fe:Mg molecular ratio exceeds 50:50. Everything else on this page is evidence for that one number.
- The 50:50 ladder. Pecora and Fahey analysed eight purified samples and measured each one’s specific gravity and indices on a split of the same powder. Ordered by iron, the five lazulites (Mg:Fe 88:12 to 61:39) read SG 3.118 to 3.190 and α 1.610 to 1.620; the three scorzalites (34:66 to 24:76) read SG 3.268 to 3.327 and α 1.633 to 1.637. Birefringence rises from 0.034 to 0.040.
- The sheets’ own analyses, by script. The lazulite sheet’s Graves Mountain analysis is 82.4% Mg of Mg + Fe2+, Pecora and Fahey’s 82:18. The scorzalite sheet’s Corrego Frio analysis is 33.8%, their 34:66. Column (2), printed identically on both sheets as Fe:Mg = 1:1, works out at exactly 50.0%: the line itself, on both pages.
- Documented failure: the line falls in a gap. No analysed sample in the paper lies between 61:39 and 34:66, so it did not measure the boundary. A straight line between the two nearest samples puts 50:50 near SG 3.222 and α 1.625, an interpolation, not a measurement, and the lazulite sheet’s own measured range already reaches 3.240. In water a 20.00 g piece reads 13.73 g at the heaviest sampled lazulite and 13.88 g at the lightest scorzalite: a 0.15 g band its samples do not reach.
- Can a hand specimen be named? Usually not. Colour fails: Pecora and Fahey found no definite correlation of colour with composition and dark blue material of both. The X-ray patterns are nearly identical on both sheets. Locality fails too: the Champion mine, California, and Hålsjöberg in Värmland appear on both sheets’ Distribution lists. Pieces far from the line can be placed by α or density; the rest need an analysis.
| Sample | Mg : Fe (molar) | Name by the 50:50 rule | SG | 20.00 g in water | α | γ | γ − α |
|---|---|---|---|---|---|---|---|
| 1. Dattas, Minas Gerais | 88 : 12 | Lazulite | 3.118 | 13.59 g | 1.610 | 1.644 | 0.034 |
| 2. Graves Mountain, Georgia (lazulite sheet, analysis (1): 82.4% Mg by script) | 82 : 18 | Lazulite | 3.122 | 13.59 g | 1.611 | 1.645 | 0.034 |
| 3. Clubbs Mountain, North Carolina | 77 : 23 | Lazulite | 3.160 | 13.67 g | 1.616 | 1.652 | 0.036 |
| 4. Black Eagle, California | 65 : 35 | Lazulite | 3.190 | 13.73 g | 1.618 | 1.654 | 0.036 |
| 5. Breyfogle Canyon, California | 61 : 39 | Lazulite | 3.190 | 13.73 g | 1.620 | 1.656 | 0.036 |
| Column (2), both sheets (50.0% Mg by script) | 50 : 50 | The line; no sample measured here | About 3.222, interpolated | About 13.79 g | About 1.625, interpolated | About 1.663 | — |
| 6. Corrego Frio, Minas Gerais (scorzalite sheet, analysis (1): 33.8% Mg by script) | 34 : 66 | Scorzalite | 3.268 | 13.88 g | 1.633 | 1.673 | 0.040 |
| 7. White Mountain, California | 27 : 73 | Scorzalite | 3.272 | 13.89 g | 1.637 | 1.677 | 0.040 |
| 8. Victory mine, South Dakota | 24 : 76 | Scorzalite | 3.327 | 13.99 g | 1.636 | 1.676 | 0.040 |
| Lazulite sheet, printed ranges | — | — | 3.122–3.240 | 13.59–13.83 g | 1.604–1.626 | 1.637–1.663 | — |
| Scorzalite sheet, printed ranges | — | — | 3.33 | 13.99 g | 1.626–1.645 | 1.663–1.680 | — |
What is the difference between lazulite and scorzalite?
One element. The September 2026 IMA list writes lazulite MgAl2(PO4)2(OH)2, status A, 1967 s.p., Austria, and scorzalite Fe2+Al2(PO4)2(OH)2, status G, 1949, Brazil. The lazulite sheet and the scorzalite sheet each say the mineral forms a series with the other, and put both in the lazulite group, with the same monoclinic space group, P21/c. The 1949 paper that named scorzalite called the series a complete isomorphous one, lazulite Mg dominant and scorzalite Fe dominant.
The rule in print. Pecora and Fahey’s 1950 paper on the series, built on eight selected specimens, six of them newly analysed, states that the name scorzalite applies only to those members whose Fe:Mg molecular ratio exceeds 50:50. Following Schaller (1930), they accept ferroan lazulite and magnesian scorzalite for the range between, calling the Graves Mountain material ferroan lazulite (Mg82:Fe18) and the White Mountain material magnesian scorzalite (Mg27:Fe73). The species pages are lazulite and scorzalite; each has its own cell-density check, not repeated here.
The 50:50 ladder: eight analyses, two names
How it was measured. Pecora and Fahey hand-picked each sample, crushed it, purified the powder with heavy liquids and a magnetic separator to over 99%, and split it: one part for the chemical analysis and a pycnometer specific gravity, the other for indices in sodium light. Their Table 2 gives the result for each sample as a molecular ratio Mg:Fe. They report that indices, specific gravity and birefringence all rise progressively with ferrous iron.
What the ladder shows. Every lazulite in the table reads SG 3.190 or less and α 1.620 or less; every scorzalite SG 3.268 or more and α 1.633 or more. Birefringence is 0.034 to 0.036 on the lazulite side and 0.040 on the scorzalite side. Worked as 20 − 20/D, a 20.00 g piece reads 13.59 to 13.73 g in water on one side and 13.88 to 13.99 g on the other.
The sheets agree with the paper. Both Handbook sheets cite it. The lazulite sheet’s analysis (1), Graves Mountain, is oxide for oxide the paper’s sample 2, and a script gives 82.4% Mg of Mg + Fe2+. The scorzalite sheet’s analysis (1), Corrego Frio, is sample 6, 33.8%. Both sheets also print the same column (2), labelled Fe:Mg = 1:1, which works out at exactly 50.0%: it is the boundary, not a specimen.
Can you tell lazulite from scorzalite without an analysis?
Only far from the line. A clean grain reading α near 1.610 is on the lazulite side of every sample in the ladder, and one reading 1.635 is on the scorzalite side. The sheets’ own ranges meet exactly at α 1.626, β 1.654 and γ 1.663, so a reading at the meeting point names nothing. A density reading works the same way: below about 13.73 g in water for 20.00 g, lazulite on this evidence; above 13.88 g, scorzalite; between, not covered by these samples. Weighing is on how to measure specific gravity at home, and matrix quartz pulls any reading down.
Documented failure: colour, pattern and place. Pecora and Fahey found no definite correlation of colour with composition: Graves Mountain, Dattas and Clubbs Mountain lazulite is light blue, but the California lazulite and scorzalite are both dark blue, and they note that specimens from quartz veins and dikes are darker blue than those in quartzite. Both sheets call the X-ray powder patterns nearly identical. Both list the Champion mine, Mono Co., California, and Hålsjöberg (Hålsjöberget on the scorzalite sheet), Värmland, so a locality label does not decide either.
Which name should the label carry?
The decision rule. With an analysis, use the 50:50 rule. Without one, the Handbook itself shows the honest form: its brazilianite and bertossaite sheets list lazulite-scorzalite among their Buranga, Rwanda, associates, naming the series rather than a member. A label reading lazulite on a dark blue pegmatite piece may be right or wrong; nothing on the specimen alone settles it.
Who each name is wrong for. Lazulite is the wrong name for the analysed Corrego Frio, White Mountain and Victory material, all 66% iron or more. Scorzalite is the wrong name for Graves Mountain and Dattas, both over 80% magnesium. Lapis lazuli is wrong for both: it is a rock, and the one-reading-or-two test that shows it is on is lazulite the same as lapis lazuli. More identification pages are in the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.