Is mimetite toxic?
Mimetite, Pb5(AsO4)3Cl, is 69.61% lead and 15.10% arsenic by mass, worked. What UK workplace texts say about each element, quoted. Not health or safety advice.
Mimetite, Pb5(AsO4)3Cl, a lead arsenate chloride, is 69.61% lead and 15.10% arsenic by mass, worked from the IMA formula. UK workplace texts treat the two elements separately: lead under the Control of Lead at Work Regulations 2002, arsenic under COSHH, whose Schedule 1 lists arsenic and whose EH40 table marks it Carc. Not advice.
In short
- What it is. The Handbook of Mineralogy mimetite sheet gives Pb5(AsO4)3Cl, hexagonal, apatite group, hardness 3.5–4, brittle, density 7.24, “a common secondary mineral in the oxidized zone of arsenic-bearing lead deposits”. The September 2026 IMA-CNMNC Master List writes the same formula, G, 1832, Germany. Worked, lead is 1036.0 and arsenic 224.76 of 1488.20: 69.61% and 15.10%, 84.72% together.
- Two elements, two places in the rules. Lead: COSHH 2002, regulation 5 says COSHH regulations 6 to 13 apply except where and to the extent the Control of Lead at Work Regulations 2002 apply, and HSE EH40/2005 Workplace exposure limits says asbestos and lead are regulated separately. Arsenic: COSHH 2002, Schedule 1 lists “Arsenic.” among substances to which the definition of carcinogen relates, and EH40 Table 1 prints arsenic and arsenic compounds except arsine (as As), notation Carc.
- The lead-and-arsenic ledger. A script matched this site’s 238 species pages with a single IMA row against the list’s formulas: 6 contain both lead and arsenic. Mimetite has the most lead (69.61%) and the most of the two together; duftite 48.56% lead and 17.56% arsenic; bayldonite, beudantite and segnitite 27 to 29% lead; ludlockite 13.53% lead and 48.91% arsenic, the most arsenic of the six.
- Documented failure: no single ranking. Ordered by lead, mimetite is first; ordered by arsenic it is fifth of six, behind ludlockite, bayldonite, segnitite and duftite. Neither order measures exposure, and EH40 itself says the absence of a substance from its list does not indicate that it is safe. This page draws no conclusion from the ledger beyond the numbers.
- Not advice. This page is not health, safety or legal advice and gives no verdict on any specimen. HSE’s page on health effects from exposure to lead covers lead at work; workplace duties are a matter for HSE, and exposure or symptoms for a clinician. The general site note is toxic minerals in a collection.
| Mineral and IMA formula | Pb, wt% | As, wt% | As atoms per Pb | Lead: UK text | Arsenic: UK text |
|---|---|---|---|---|---|
| Mimetite, Pb5(AsO4)3Cl | 69.61 | 15.10 | 0.6 | CLAW 2002 (EH40 para. 52) | COSHH Sched. 1; EH40 Table 1, Carc |
| Mimetite, Phoenixville, Pennsylvania (sheet analysis) | 69.23 | 15.11 | 0.60 | CLAW 2002 | COSHH Sched. 1; EH40 Table 1, Carc |
| Duftite, PbCu(AsO4)(OH) | 48.56 | 17.56 | 1 | CLAW 2002 | COSHH Sched. 1; EH40 Table 1, Carc |
| Beudantite, PbFe3+3(AsO4)(SO4)(OH)6 | 29.11 | 10.53 | 1 | CLAW 2002 | COSHH Sched. 1; EH40 Table 1, Carc |
| Bayldonite, Cu3PbO(AsO3OH)2(OH)2 | 28.47 | 20.59 | 2 | CLAW 2002 | COSHH Sched. 1; EH40 Table 1, Carc |
| Segnitite, PbFe3+3(AsO4)(AsO3OH)(OH)6 | 27.42 | 19.83 | 2 | CLAW 2002 | COSHH Sched. 1; EH40 Table 1, Carc |
| Ludlockite, PbFe3+4As3+10O22 | 13.53 | 48.91 | 10 | CLAW 2002 | COSHH Sched. 1; EH40 Table 1, Carc |
Is mimetite toxic? What it is made of, worked
A lead arsenate chloride, about seven-tenths lead. The Handbook of Mineralogy mimetite sheet gives Pb5(AsO4)3Cl and prints its ideal composition as As2O5 23.17, PbO 74.99 and Cl 2.38, less 0.54 for oxygen equivalent to chlorine. With Pb 207.2, As 74.9216, O 15.999 and Cl 35.45, the formula mass is 1488.20; lead is 69.61%, arsenic 15.10%, oxygen 12.90% and chlorine 2.38%, and the same arithmetic reproduces each printed oxide. These figures agree with is mimetite UV reactive and is pyromorphite toxic.
The specimen the sheet analysed. The sheet’s analysis (1), from Phoenixville, Pennsylvania, prints PbO 74.58, As2O5 23.17, P2O5 0.14 and Cl 2.39, total 99.74. Worked, that is 69.23% lead, 15.11% arsenic and 0.061% phosphorus; phosphorus takes about 1% of the arsenate sites. Here the formula and the specimen agree closely. The sheet records no hazard wording of any kind, and this page does not supply one.
Lead and arsenic: what UK workplace texts say about each
Lead. The Control of Lead at Work Regulations 2002, regulation 2, read on legislation.gov.uk on 12 November 2026 in its latest available revised form, defines lead as lead (including lead alkyls, lead alloys, any compounds of lead and lead as a constituent of any substance or material) which is liable to be inhaled, ingested or otherwise absorbed by persons, with an exception for vehicle exhausts on a road. COSHH 2002, regulation 5 says regulations 6 to 13 apply except where and to the extent that the Control of Lead at Work Regulations 2002 apply, and EH40/2005 paragraph 52 reads: “Asbestos and lead are regulated separately”. How that definition and CLAW’s own limit read for a lead carbonate is on is cerussite toxic and is not repeated here.
Arsenic. COSHH 2002, Schedule 1, headed Other substances and processes to which the definition of “carcinogen” relates, lists “Arsenic.”; COSHH 2002, regulation 2 defines a carcinogen to include a substance or mixture referred to in Schedule 1. EH40/2005 (fourth edition, 2020) Table 1 prints “Arsenic and arsenic compounds except arsine (as As)”, a long-term limit of 0.1 mg.m-3 over the 8-hour reference period, no short-term figure, and the notation Carc, which it defines as capable of causing cancer and/or heritable genetic damage. Its paragraph 51 says regulation 7(5) of COSHH sets out requirements for the control of exposure to carcinogenic and mutagenic substances. These are workplace air limits and definitions expressed as arsenic; this page does not convert them into amounts of mimetite, and they are not a threshold for a specimen.
What EH40 does not do. A text search of EH40 finds no occurrence of the word mimetite. The same approach to an arsenic sulfide, with its sheet associates, is on is orpiment toxic; mimetite’s case differs in carrying lead as well, which EH40 sends elsewhere.
Does mimetite have more arsenic than other lead minerals?
The lead-and-arsenic ledger, method. A script listed every species page on this site, including this run’s duftite and tsumebite, took the 238 whose slug matches a single row on the September 2026 IMA list, and kept those whose formula contains both the symbols Pb and As. Six remain: mimetite, duftite, bayldonite, beudantite, segnitite and ludlockite. The 22 pages for group, series or variant names (apatite, tourmaline, tennantite and others) were not tested, so the six are a count over the 238, not over the site or the mineral kingdom.
Result. By lead, mimetite is first at 69.61%, then duftite 48.56%, beudantite 29.11%, bayldonite 28.47%, segnitite 27.42% and ludlockite 13.53%. By arsenic the order reverses almost completely: ludlockite 48.91%, bayldonite 20.59%, segnitite 19.83%, duftite 17.56%, mimetite 15.10%, beudantite 10.53%. Mimetite has three arsenic atoms for every five lead; ludlockite ten for every one.
Documented failure: the ranking shortcut. It would be easy to read either column as a ranking of danger. Each ranks composition only, the two orders disagree, and neither describes exposure. Galena, cerussite and pyromorphite, on is galena toxic, is cerussite toxic and is pyromorphite toxic, carry more lead than mimetite and no arsenic in their formulas; the lead apatite comparison is on the pyromorphite page and the two-metal case of lead with copper on is linarite toxic.
Is mimetite rare, fluorescent or radioactive?
Rare? No, by its sheet: “A common secondary mineral in the oxidized zone of arsenic-bearing lead deposits”, with many localities, of which the sheet names Johanngeorgenstadt, Saxony; Příbram, Czech Republic; a number of localities in Cornwall; Dry Gill and other mines, Caldbeck Fells, Cumbria; Leadhills, Lanarkshire; extraordinary crystals at Tsumeb, Namibia; Gowde, Iran; Phoenixville, Pennsylvania, and mines in Arizona and Utah; Santa Eulalia, San Pedro Corallitos and the Ojuela mine, Mexico; Broken Hill and the Mt. Bonnie mine, Australia; and Hat Yai, Thailand.
Fluorescent? The sheet says piezoelectric; may fluoresce reddish yellow under LW or SW UV. What that wording means for a lamp test is on is mimetite UV reactive. Radioactive? Its IMA formula has no uranium, thorium or potassium, and the sheet prints no radioactivity; the general method is on is my mineral radioactive.
Mimetite or pyromorphite? The sheet says the name is from the Greek for an imitator, as it imitates pyromorphite. A label reading pyromorphite does not show a specimen is free of arsenic; separating the two is worked on how to tell pyromorphite from mimetite. The sheet also names a dimorph, clinomimetite; the September 2026 IMA list has no clinomimetite row, and the composition figures here depend only on the formula.
Where should questions about mimetite go?
Not to this page. It reports a formula, a sheet and the wording of UK texts. It gives no verdict on mimetite or any specimen, and no handling, cleaning, storage, cutting or display advice; nothing here says any amount, form or use of mimetite is safe. HSE’s page on health effects from exposure to lead sets out what HSE says about lead at work. Workplace duties belong with HSE; exposure or symptoms with a clinician. This is not health, safety or legal advice.
Where to go next. The species is on mimetite; the other hazard pages are is pyromorphite toxic, is orpiment toxic and is cerussite toxic; the general note is toxic minerals in a collection, and more guides are in the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.