Crandallite
Crandallite, CaAl3(PO4)(PO3OH)(OH)6: hexagonal calcium aluminium phosphate, hardness 5, density 2.78–3.04, with Sr goyazite and Ba gorceixite. Sheet data.
Crandallite is a calcium aluminium phosphate, CaAl3(PO4)(PO3OH)(OH)6 on the September 2026 IMA list: hexagonal, hardness 5, measured density 2.78 to 3.04, yellow, white or grey, usually as crusts and nodules rather than crystals. Goyazite (Sr), gorceixite (Ba) and plumbogummite (Pb) share the formula with one cation changed; analyses decide which name applies.
In short
- The species. The September 2026 IMA-CNMNC Master List lists crandallite as CaAl3(PO4)(PO3OH)(OH)6, status Rd, 1999 s.p., USA. The Handbook of Mineralogy sheet gives hexagonal R3̄m, crystals only to 1 mm, commonly colloform to pulverulent crusts, nodular or massive; perfect {0001} cleavage, hardness 5, density 2.78 to 3.04, uniaxial (+). A 20.00 g piece reads 12.81 to 13.42 g in water.
- The group, by script. A field scan of the IMA formula column finds 4 rows written XAl3(PO4)(PO3OH)(OH)6: crandallite (Ca), goyazite (Sr), gorceixite (Ba) and plumbogummite (Pb). Allowing Fe3+ or V3+ for Al and arsenate for phosphate, the same shape has 14 rows. The crandallite and goyazite sheets print “Crandallite group”; the gorceixite sheet, revised in 2020, prints “Alunite supergroup, plumbogummite group”.
- The A-cation ledger. Recast from the sheets’ oxide analyses, the Alto Benedito, Brazil, crandallite is Ca 0.558 to Sr 0.442, which reproduces the printed 0.56:0.44 and gives exactly 1.000 large cation and 2.998 Al per 2 P. The two goyazite analyses are 87% and 68% Sr; the two gorceixite analyses 98.6% and 98.3% Ba. Ca at 56% is the narrowest margin of the six.
- Documented failures. The Brooklyn mine, Utah, analysis gives only 0.81 large cation per 2 P, with 3.80% SO3 and 35.13% insolubles deducted, so it does not recast to the formula. And the cell check works for crandallite (2.996 against the printed 3.00) but not for its partners: 3.258 against 3.29 for goyazite and 3.422 against 3.389 for gorceixite.
- Utah and wavellite. The sheet names three Utah localities: the Brooklyn mine, Tintic district; the Little Green Monster mine, Clay Canyon, near Fairfield; and Amatrice Hill. The wavellite sheet lists crandallite as an associate, and the variscite sheet lists it at the Little Green Monster mine.
| Row or analysis | Formula or source | Ca : Sr : Ba (moles) | Large cation per 2 P | Al per 2 P | Density printed | Density from cell, worked | Reads as |
|---|---|---|---|---|---|---|---|
| Crandallite, ideal | CaAl3(PO4)(PO3OH)(OH)6; Rd 1999 s.p., USA | 1 : 0 : 0 | 1 | 3 | 2.78–3.04 meas.; 3.00 calc. | 2.996 (a 7.0062, c 16.192 Å) | Reproduces |
| Crandallite (2), Alto Benedito pegmatite, Brazil | Crandallite sheet; printed Ca:Sr = 0.56:0.44 | 0.558 : 0.442 : 0 | 1.000 | 2.998 | — | — | Crandallite, Ca by 11.6 points |
| Crandallite (1), Brooklyn mine, Utah | Crandallite sheet; 35.13% insolubles deducted; SO3 3.80, MgO 0.94 | 0.862 : 0.138 : 0 | 0.813 | 3.979 | — | — | Does not recast to the formula |
| Goyazite, ideal | SrAl3(PO4)(PO3OH)(OH)6; Rd 1999 s.p., Brazil | 0 : 1 : 0 | 1 | 3 | 3.26 meas.; 3.29 calc. | 3.258 (a 7.015, c 16.558 Å) | Printed calc. does not reproduce |
| Goyazite (1), Oxford Co., Maine; (2) Alto Bernardino, Brazil | Goyazite sheet | 0 : 0.872 : 0.128; 0.168 : 0.675 : 0.157 | 1.001; 1.040 | 3.110; 3.266 | — | — | Goyazite, both Sr-led |
| Gorceixite, ideal | BaAl3(PO4)(PO3OH)(OH)6; G 1906, Brazil | 0 : 0 : 1 | 1 | 3 | 3.036–3.185 meas.; 3.389 calc. | 3.422 (a 7.0538, c 17.2746 Å) | Printed calc. does not reproduce |
| Gorceixite (1), Sydney Basin; (2) Crosscut Creek, Yukon | Gorceixite sheet | 0 : 0.014 : 0.986; 0.005 : 0.012 : 0.983 | 0.965; 1.028 | 2.999; 2.961 | — | — | Gorceixite, both Ba-led |
| Plumbogummite, ideal | PbAl3(PO4)(PO3OH)(OH)6; Rd 1999 s.p., France | Pb | 1 | 3 | No sheet cached | — | IMA row only |
What is crandallite? Its formula and IMA status
Crandallite is CaAl3(PO4)(PO3OH)(OH)6 on the September 2026 IMA list, status Rd (redefined), 1999 s.p., with the USA as the country of first description. The list’s first reference is American Journal of Science 43 (1917), 69, and its second Mineralogical Magazine 75 (2011), 145. The Handbook of Mineralogy crandallite sheet prints the same formula and gives the ideal composition as P2O5 34.28, Al2O3 36.94, CaO 13.55 and H2O 15.23, which the script reproduces to within 0.01 (CaO works out at 13.54). Worked, the mineral is 9.68% calcium, 19.55% aluminium and 14.96% phosphorus by mass.
What the sheet records. Hexagonal, point group 3̄ 2/m, space group R3̄m, a = 7.0062 and c = 16.192 Å, Z = 3. Crystals are trigonal prisms terminated by {0001}, or pseudocubic rhombohedra, to 1 mm; it also forms rosettes of fibres, spherules and crusts with radial fibrous structure, and is commonly colloform to pulverulent, nodular or massive. Cleavage perfect on {0001}; brittle; hardness 5; density 2.78 to 3.04 measured, 3.00 calculated. Yellow, white or grey, colourless in thin section; streak white; vitreous, dull to chalky when massive; uniaxial (+), ω 1.613 to 1.627, ε 1.622 to 1.632.
Where it forms. The Occurrence field: in weathered phosphatic aluminous sedimentary rocks and carbonatites; in phosphate-rich nodules; from complex granite pegmatites; in amphibolite-grade metaquartzites; and as an authigenic mineral in anoxic marine sediments or in clay-rich sediment beneath a tropical swamp. Its associates are fluorapatite (an apatite-group species), hydroxylherderite and quartz.
What is the crandallite group?
Four formulas, one cation apart. A field scan of the formula column of the IMA list, confirmed by a whole-text token search, finds four rows written XAl3(PO4)(PO3OH)(OH)6: crandallite with calcium, goyazite with strontium (Rd, 1999 s.p., Brazil), gorceixite with barium (G, 1906, Brazil) and plumbogummite with lead (Rd, 1999 s.p., France). Widening the pattern to allow Fe3+ or V3+ in place of aluminium and arsenate in place of phosphate gives 14 rows, among them arsenocrandallite, benauite, kintoreite and springcreekite. The list itself carries no group column, so these counts are of formula shape, not of an official membership.
Two sheets, two group names. The crandallite and goyazite sheets, dated 2001–2005, print “Mineral Group: Crandallite group.” The gorceixite sheet, revised 12/8/2020, prints “Alunite supergroup, plumbogummite group.” Both labels are quoted as printed; this page does not choose between them.
Weight, worked. Swapping the cation changes the mass far more than the cell. Goyazite’s formula is 11.48% heavier than crandallite’s and its cell 2.52% larger; gorceixite’s is 23.49% heavier and its cell 8.14% larger. A 20.00 g piece reads 12.81 to 13.42 g in water as crandallite, 13.87 g as goyazite (3.26) and 13.41 to 13.72 g as gorceixite (3.036 to 3.185), on the method at how to measure specific gravity at home. The ranges touch, so weight alone does not name the species.
Crandallite, goyazite or gorceixite? The A-cation ledger
Method. Each oxide weight on the three sheets was divided by its formula weight on standard atomic weights, and calcium, strontium and barium compared as moles, with phosphorus set to 2 and aluminium reported on the same basis. The table above shows every analysis the three sheets print.
What it shows. The Alto Benedito pegmatite, Paraíba, Brazil, analysis on the crandallite sheet gives Ca 0.558 to Sr 0.442, which is the sheet’s printed Ca:Sr = 0.56:0.44, with 1.000 large cation and 2.998 aluminium per 2 phosphorus: a clean fit to the formula. Its third reference is titled “Strontian crandallite from the Alto Benedito pegmatite”. Calcium leads by 11.6 points, the narrowest of the six analyses. The goyazite analyses from Oxford Co., Maine, and Alto Bernardino, Brazil, are 87% and 68% strontium, the second with 17% calcium and 16% barium; the gorceixite analyses from the Sydney Basin, Australia, and Crosscut Creek, Yukon, are over 98% barium.
Documented failure: the Brooklyn mine analysis. The Utah analysis, printed after deducting 35.13% insolubles as quartz, barite and sulfides, carries 3.80% SO3 and 0.94% MgO and recasts to only 0.813 large cation per 2 phosphorus, with 3.979 aluminium. It is calcium-led (86%), but it does not reproduce the formula, and the sheet gives no reason. A second failure is in the cells: crandallite’s gives 2.996 against the printed 3.00, but goyazite’s gives 3.258 against 3.29 and gorceixite’s 3.422 against 3.389. The arithmetic is reported; the sheets are not corrected.
Where is crandallite found? Utah and the sheet’s list
Distribution, as printed. In Utah: the Brooklyn mine, near Silver City, Tintic district, Juab Co.; the Little Green Monster mine, Clay Canyon, about nine km west of Fairfield; and Amatrice Hill, about 40 km northwest of Fairfield, Utah Co. Elsewhere in the USA: the Palermo #1 and Fletcher mines, near North Groton, New Hampshire; near Gore, Virginia; Dug Hill, near Avant, Arkansas; several rock formations in central and northern Florida; and the Everly, Hugo and Tip Top mines, South Dakota. Abroad: the Alto Benedito pegmatite, Paraíba, Brazil; Blaton, Belgium; Ronneburg, Thuringia, Germany; Wheal Jane, Kea, Cornwall; Fort Lismeenagh, Co. Limerick, Ireland; the Kovdor massif, Kola Peninsula, Russia; in Australia, the Iron Monarch quarry, Iron Knob, and the Moculta phosphate quarry; and the Buranga pegmatite, Rwanda.
With wavellite and variscite. Wavellite’s sheet gives its associates as “Crandallite, variscite”, and the variscite sheet lists crandallite first among its associates at the Little Green Monster mine, Utah, where goyazite is also named. The Florida phosphate setting is discussed on is wavellite radioactive; reading an assemblage like this is the subject of what is mineral paragenesis.
Name, not type locality. The name honours Milan L. Crandall, Jr., mining engineer, of Provo, Utah; type material is at the National Museum of Natural History, Washington, D.C., R5641. The sheet marks no type locality and the IMA list gives the USA; the term is explained at what is a type locality. More phosphates are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.