Chlorapatite
Chlorapatite is the chlorine apatite, Ca5(PO4)3Cl: hexagonal or monoclinic, hardness about 5, density 3.17–3.18, 6.81% chlorine. Its cells, places and silences.
Chlorapatite is Ca5(PO4)3Cl, the chlorine-dominant member of the apatite group, on the September 2026 IMA list and its Handbook sheet: prismatic hexagonal crystals to 5 cm, hardness about 5, density 3.17–3.18, greenish yellow to pinkish white. Worked, it is 6.81% chlorine. The sheet calls it relatively much rarer than fluorapatite or hydroxylapatite.
In short
- The species. The Handbook of Mineralogy sheet gives hexagonal or monoclinic symmetry, prismatic hexagonal crystals to 5 cm, granular or massive habit, poor cleavage on {0001} and {10-10}, brittle, hardness about 5, density 3.17–3.18, vitreous, greenish yellow, pinkish white or light greenish gray, uniaxial (−) and sometimes biaxial (−). The September 2026 IMA-CNMNC Master List row reads Ca5(PO4)3Cl, Rn, 2010 s.p. It is one of three calcium members of the apatite group.
- The two-cell check. The hexagonal cell, a = 9.5979 and c = 6.7762 Å, holds 540.59 ų; two formula units of 520.75 g/mol give 3.199. The monoclinic cell, a = 9.605, b = 19.210 (exactly 2a), c = 6.785 Å at 120°, holds 1084.19 ų, twice as much. At the printed Z = 6 it gives 4.785, 1.5 times the measured 3.17–3.18; at Z = 4 it gives 3.190. Neither cell reproduces the printed 3.172 exactly.
- Heavier but roomier. Against fluorapatite’s hexagonal cell, chlorapatite’s formula is 3.26% heavier but its cell is 2.77% larger: a is 2.13% longer and c 1.48% shorter. Worked, the cell density rises only 0.48%, 3.184 to 3.199. That is why the measured ranges overlap and density cannot name an apatite; the separating numbers are on fluorapatite vs chlorapatite.
- Documented failure: Bob’s Lake. The sheet’s analysis (1) and its X-ray pattern come from Bob’s Lake, Canada. Its Distribution places Bob’s Lake in “Frontenac Co., Quebec”, while its own reference (4) is Hounslow and Chao (1970), “Monoclinic chlorapatite from Ontario”. One place cannot be in both provinces; this page writes Bob’s Lake, Frontenac Co., Canada, and does not choose.
- What the sheet does not print. No luminescence, no magnetism, no streak, no radioactivity and no use. USGS Open-File Report 99-529, Table 1 has no chlorapatite row; its “Apatite” row (8 samples) gives a best range above 1.70 amps. The formula carries no uranium or thorium; see is apatite radioactive.
| Cell (sheet) | Space group | a, b, c (Å) | Angle (printed) | Z | Volume (ų) | Density from cell | Printed density |
|---|---|---|---|---|---|---|---|
| Chlorapatite, hexagonal | P63/m | 9.5979, —, 6.7762 | — | 2 (printed) | 540.59 | 3.199 | Meas. 3.17–3.18 |
| Chlorapatite, monoclinic | P21/b | 9.605, 19.210, 6.785 | β = 120° | 6 (printed) | 1084.19 | 4.785 | Calc. 3.172 (monoclinic) |
| Chlorapatite, monoclinic | P21/b | 9.605, 19.210, 6.785 | β = 120° | 4 (worked) | 1084.19 | 3.190 | — |
| Fluorapatite, hexagonal | P63/m | 9.3973, —, 6.8782 | — | 2 (printed) | 526.03 | 3.184 | Calc. 3.18; meas. 3.1–3.25 |
| Fluorapatite, monoclinic | P21/b | 9.4877, 18.9628, 6.8224 | β = 119.97° | 6 (printed) | 1063.32 | 4.725 (3.150 at Z = 4) | — |
| Hydroxylapatite, hexagonal | P63/m | 9.4166, —, 6.8745 | — | 2 (printed) | 527.91 | 3.160 | Calc. 3.16; meas. 3.14–3.21 |
What is chlorapatite? The chlorine member of the apatite group
Chlorapatite is Ca5(PO4)3Cl, the apatite-group calcium phosphate in which chlorine is the dominant anion at the site that also takes fluorine and hydroxyl. The Handbook of Mineralogy chlorapatite sheet files it under Apatite group; Cl > F or OH, and names it for dominant chlorine and membership in the apatite group. The September 2026 IMA-CNMNC Master List row is Ca5(PO4)3Cl, status Rn (renamed), 2010 s.p., with the country given as Austria / Germany / Spain / Switzerland. How the three calcium apatites are told apart from an analysis, and why an unanalysed label should stay “apatite”, is set out on the apatite page; this page does not repeat it.
The properties, as printed. Prismatic hexagonal crystals to 5 cm; granular, massive, and it may be in zoned intergrowths with fluorapatite. Cleavage poor on {0001} and {10-10}, tenacity brittle, hardness about 5, measured density 3.17–3.18 and calculated 3.172 (monoclinic). It is transparent to translucent, greenish yellow, pinkish white or light greenish gray, with a vitreous lustre. The optical class is uniaxial (−), may be biaxial (−): ω = 1.650–1.667 and ε = 1.647–1.665, read from the rendered sheet because the text extraction drops ε; the biaxial figures are α = 1.665, β = 1.667, γ about 1.667, 2V about 10°.
Composition, worked. On standard atomic weights the molar mass is 520.75 g/mol: chlorine 6.81% by mass, P2O5 40.89% and CaO 53.84%, with a −O = Cl2 correction of 1.54. Those are the four figures of the sheet’s ideal column, and they total 100.00. The Bob’s Lake analysis prints 6.2% chlorine, 0.91 of the ideal, and the Fairfax, Virginia analysis 3.22%.
Is chlorapatite hexagonal or monoclinic? The two-cell check
Both: the sheet prints a hexagonal and a monoclinic cell and says end-member chlorapatite is monoclinic, but its monoclinic cell only fits the density with four formula units, not the six it prints. The hexagonal cell, P63/m, a = 9.5979 Å and c = 6.7762 Å, has a volume of (√3/2)·a²·c = 540.59 ų, and two formula units give 2 × 520.75 ÷ (0.60221 × 540.59) = 3.199. The monoclinic cell, P21/b, a = 9.605, b = 19.210, c = 6.785 Å with the angle printed as β = 120°, has a·b·c·sin 120° = 1084.19 ų. Its b is exactly twice a, and its volume is 2.006 times the hexagonal cell’s.
Documented failure: Z = 6. Six formula units in 1084.19 ų give 4.785, half as heavy again as the measured 3.17–3.18. Four give 3.190, 0.3% above the top of the measured range, which is what a cell twice the hexagonal one should hold. The fluorapatite sheet prints the same pattern: its monoclinic cell gives 4.725 at the printed Z = 6 and 3.150 at Z = 4, while its hexagonal cell gives 3.184 against a printed 3.18. Neither chlorapatite cell gives the printed calculated density, 3.172, exactly; this page reports the arithmetic and does not correct the sheet.
Heavier but roomier. Chlorine is heavier than fluorine, so chlorapatite’s formula is 3.26% heavier than fluorapatite’s, but its hexagonal cell is 2.77% larger: a is 2.13% longer and c 1.48% shorter. The cell density rises only 0.48%, from 3.184 to 3.199, which is why the two measured ranges overlap. A 20.00 g chlorapatite reads 13.69–13.71 g in water, inside fluorapatite’s 13.55–13.85 g; the method is how to measure specific gravity at home.
Is chlorapatite magnetic, fluorescent or radioactive? What the sheet prints
The chlorapatite sheet is silent on all three. A ligature-aware search of its text finds no luminescence wording, no magnetism and no radioactivity; the same searches match the hemimorphite and willemite sheets (fluorescence) and the magnetite sheet (“Strongly magnetic”), the positive controls. Silence on a sheet is not a test result.
Magnetic. USGS Open-File Report 99-529, Table 1, by Rosenblum and Brownfield, lists no chlorapatite, fluorapatite or hydroxylapatite. Its “Apatite” row, 8 samples, gives a total range of 1.40 to above 1.70 amps and a best range above 1.70 on a Frantz separator. The report defines “diamagnetic” as nonmagnetic at 1.70 amps. That row does not say which apatite species were run; the background is on which minerals are magnetic.
Fluorescent and radioactive. Of the three calcium apatite sheets only fluorapatite’s mentions luminescence (“May be cathodoluminescent, phosphorescent, or fluorescent in UV”); the rest is on is apatite fluorescent and fluorescent minerals explained. Ca5(PO4)3Cl contains no uranium or thorium; trace uranium in real apatite is covered on is apatite radioactive, and radioactivity questions go to is my mineral radioactive. Neither is advice.
Where is chlorapatite found? Snarum, Bushveld, Virginia and more
The sheet calls chlorapatite relatively much rarer than fluorapatite or hydroxylapatite, formed in F-deficient environments. It names calcsilicate marble; an accessory mineral in layered mafic intrusions; veins through diabase; triphylite replaced by it in granite pegmatite; and meteorites. Its associations are actinolite, diopside, calcite, quartz and talc at Bob’s Lake; amphibole, chlorite, plagioclase, titanite and datolite at the Bull Run quarry, Virginia; and olivine, orthopyroxene, phlogopite, ferroalluaudite and chromite at the Angarf-Sud pegmatite, Morocco.
The Distribution field, as printed (“analyzed material noted from”). In the USA, the Fairfax quarry, Centreville, Fairfax Co., and the Bull Run quarry, Loudoun Co., Virginia; the Stillwater complex, Montana; the White Picacho district, Maricopa and Yavapai Cos., Arizona. Bob’s Lake, Frontenac Co., Canada (printed “Quebec”; see above). The Bushveld complex, Transvaal, South Africa. The Angarf-Sud pegmatite, Tazenakht Plain, Morocco. Rajagarh, near Ajmer, Rajasthan, India. Kurokura, Kangway Prefecture, Japan. Kragerø and Ødegården, Bamble, and as large crystals from Snarum, Norway. The sheet marks no type locality, and we add no locality.
Uses. The sheet prints no use for chlorapatite, and this page claims none; the fluorapatite sheet’s “An important ore in carbonatites” is about fluorapatite. Related species are at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.