Matlockite
Matlockite is lead fluoride chloride, PbFCl: tetragonal, tabular on {001}, perfect cleavage, hardness 2.5–3, density 7.12. Its cell, its lookalikes, its places.
Matlockite is lead fluoride chloride, PbFCl on its Handbook sheet and PbClF on the September 2026 IMA list: tetragonal, tabular on {001} with a perfect {001} cleavage, hardness 2.5–3, density 7.12. Worked from standard atomic weights it is 79.19% lead. It is named for its first occurrence near Matlock, Derbyshire; the sheet marks no type locality.
In short
- The species. The Handbook of Mineralogy sheet gives tetragonal, tabular crystals to 5 cm flattened on {001}, a perfect {001} cleavage with pearly lustre on it, hardness 2.5–3, density 7.12, brittle, colourless to amber-yellow and adamantine. The September 2026 IMA-CNMNC Master List writes it PbClF, status G, 1851, United Kingdom; the sheet writes PbFCl.
- The cell check. The sheet prints a = 4.1104 Å, c = 7.2325 Å and Z = 2. Worked, a²c is 122.20 ų, and two formula units of 261.65 g/mol in that volume give a density of 7.11. The measured density is 7.12; the printed calculated density, 7.16, does not follow from the printed cell.
- Documented failure: the 17-gram cluster. A 20.00 g piece reads 17.19 g in water as matlockite, 17.16 g as pyromorphite and 17.24 g as mendipite: 0.03 g and 0.05 g apart. The balance separates phosgenite, at 16.73–16.75 g, and cerussite, at 16.95 g. It cannot separate these three; system, cleavage and optics can.
- Where it is found. The sheet gives large crystals from the Bage and Wallclose mines, about 2.5 km south of Matlock, Derbyshire; slag at Laurium, Greece, at Baratti Beach and near Campiglia, Tuscany, and at the Argent mines, South Africa; fine crystals from the Mammoth-St. Anthony mine, Tiger, Arizona; and sites in Germany, Peru and Chile.
| Species | IMA formula | System | Hardness | Cleavage (sheet) | Density (meas.) | 20.00 g in water | Difference from matlockite | Pb by mass |
|---|---|---|---|---|---|---|---|---|
| Matlockite | PbClF | Tetragonal | 2.5–3 | {001} perfect | 7.12 | 17.19 g | — | 79.19% |
| Pyromorphite | Pb5(PO4)3Cl | Hexagonal | 3.5–4 | On {10-11}, interrupted | 7.04 | 17.16 g | 0.03 g lighter | 76.38% |
| Mendipite | Pb3O2Cl2 | Orthorhombic | 2.5 | {010} perfect | 7.240 | 17.24 g | 0.05 g heavier | 85.80% |
| Cerussite | Pb(CO3) | Orthorhombic | 3–3.5 | {110} and {021} good | 6.55 | 16.95 g | 0.24 g lighter | 77.54% |
| Phosgenite | Pb2(CO3)Cl2 | Tetragonal | 2–3, varying with direction | {001} and {110} distinct | 6.12–6.15 | 16.73–16.75 g | 0.44–0.46 g lighter | 75.99% |
What is matlockite? A lead fluoride chloride with one perfect cleavage
Matlockite is PbFCl, a soft, heavy, adamantine lead mineral that carries both fluorine and chlorine. The Handbook of Mineralogy matlockite sheet gives tetragonal crystals, point group 4/m 2/m 2/m, tabular and flattened on {001}, with {110}, {011} and {111} modifications, to 5 cm; they may be equant or rounded, and grow in subparallel, rosettelike, radiating and hemispherical aggregates, or lamellar, cleavable masses. Cleavage is perfect on {001}, fracture uneven to subconchoidal, tenacity brittle, hardness 2.5–3, density 7.12 measured. It is colourless, pale yellow, amber-yellow or yellow-orange, adamantine and pearly on {001}.
What the IMA list records. The September 2026 IMA-CNMNC Master List row reads matlockite, PbClF, status G (grandfathered), 1851, United Kingdom, with Mineralogical Magazine 60 (1996), 833 as its second reference. The sheet heads the same composition PbFCl. Worked from standard atomic weights the molar mass is 261.65 g/mol, of which lead is 79.19%, fluorine 7.26% and chlorine 13.55%; the sheet’s ideal column prints those three numbers. Its Cromford analysis works out at 0.975 fluorine and 0.987 chlorine per lead, and its Tiger analysis at 1.002 and 1.005.
Name and type material. The sheet says the name is for the first occurrence near Matlock, England, and puts type material at the Natural History Museum, London, number 89055. It marks no type locality, so this page names none; the term is explained at what a type locality is. It forms in the oxide zone of some lead-bearing mineral deposits, with phosgenite, anglesite, cerussite, galena, sphalerite, barite and fluorite at Cromford, and with diaboleite, boleite, caledonite and leadhillite at Tiger, Arizona.
What is the structure of matlockite? What the sheet prints, and a cell check
The sheet gives matlockite’s structure as tetragonal, space group P4/nmm, a = 4.1104 Å, c = 7.2325 Å, with two formula units in the cell, measured on synthetic material. Its strongest X-ray powder lines, also synthetic, are 3.574 (100), 2.906 (45) and 3.617 (40). The sheet’s optical class is uniaxial (−), ω = 2.145 and ε = 2.006, rarely biaxial due to strain. The ε figure was read from the rendered sheet, because the text extraction drops the symbol. The difference, 0.139, is worked here; the sheet prints the two indices.
The cell check. The volume of a tetragonal cell is a²c: 4.1104² × 7.2325 = 122.20 ų. Two formula units of 261.65 g/mol in that volume give 2 × 261.65 ÷ (0.60221 × 122.20) = 7.11 g/cm³. The measured density is 7.12. The sheet prints 7.16 as its calculated density, which the printed cell does not reproduce; this page reports both rather than choosing. The full refinement is the sheet’s reference (2), Pasero and Perchiazzi (1996), Mineralogical Magazine 60, 833–836; no copy could be fetched for this page, so it describes the structure no further than the sheet does.
Formula relatives, not structure claims. A script over the September 2026 IMA list for formulas made of one cation, one chlorine and one fluorine, cross-checked by a raw line scan, finds 3: matlockite, PbClF; rorisite, CaClF (A, 1989-015, Russia); and zhangpeishanite, BaFCl (A, 2006-045, China). Laurelite, Pb7F12Cl2, has the same three elements in other proportions. The scan matches formulas only; it says nothing about whether those minerals share matlockite’s structure.
Matlockite, pyromorphite or mendipite? The 17-gram cluster
Documented failure: weight cannot separate matlockite from pyromorphite or mendipite. Worked as 20 − 20/D, a 20.00 g piece reads 17.19 g in water as matlockite, 17.16 g as pyromorphite and 17.24 g as mendipite. The gaps, 0.03 g and 0.05 g, are smaller than a crack, a matrix fleck or a trapped bubble can shift a reading. Method: how to measure specific gravity at home. All three can be pale: the pyromorphite sheet includes yellow and may be colorless, and the mendipite sheet gives colorless to white, tinged yellow among other tints.
What the sheets separate them on. Matlockite is tetragonal and uniaxial (−), with a perfect {001} cleavage and a pearly lustre on it. Pyromorphite is hexagonal and uniaxial (−), harder at 3.5–4, with an interrupted cleavage on {10-11}, and its crystals are prismatic with hoppered terminations typical. Mendipite is orthorhombic and biaxial (+), hardness 2.5, cleavage perfect on {010}, in columnar or fibrous aggregates and cleavable masses, pearly to silky on cleavages.
What the balance does separate. phosgenite, the other tetragonal lead mineral on matlockite’s Cromford association line, reads 16.73–16.75 g, 0.44–0.46 g lighter, and is sectile where matlockite is brittle. cerussite reads 16.95 g, 0.24 g lighter, and is orthorhombic and very brittle. anglesite reads 16.87 g.
Where is matlockite found? Matlock, slag heaps and Tiger, Arizona
The matlockite sheet’s Distribution field opens with Derbyshire. Large crystals from the Bage and Wallclose mines, about 2.5 km south of Matlock, Derbyshire, England. In slag at Laurium, Greece; in slag along Baratti Beach and one km north of Campiglia, Tuscany, Italy; at the Argent Pb–Zn mines, about 100 km east of Johannesburg, South Africa, in slag. From the Christian-Levin mine near Essen, Germany. Fine crystals from the Mammoth-St. Anthony mine, Tiger, Pinal Co.; the Apache mine, Gila Co.; and the Mildren mine, Cabibi district, Arizona. At Chancay, Peru, and Challacollo, Tarapacá, Chile.
Shared with laurionite. Laurium slag, Baratti Beach and the Argent mines also appear on the laurionite sheet, which calls that mineral an alteration product of slag. Matlockite is also named as an associate on the sheets of boleite, cotunnite, hydrocerussite, paralaurionite and phosgenite.
Matlockite is 79.19% lead by mass; lead is covered on toxic minerals in a collection, and this page is not health or safety advice. 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.