Is arsenopyrite magnetic?
Arsenopyrite, FeAsS, is not magnetic like magnetite: its USGS best range is above 1.70 amp. Of 18 arsenic species tabled, 17 stay behind; renierite is pulled.
No, not in the way magnetite is. Arsenopyrite, FeAsS, hardness 5.5 to 6, has no magnetic property on its Handbook sheet, and USGS Open-File Report 99-529 gives its 3 samples a best range above 1.70 amp, diamagnetic by its definitions. Of 18 arsenic minerals in the same table, 17 stay behind; renierite is the one pulled.
In short
- Diamagnetic by its best range. USGS defines diamagnetic minerals as nonmagnetic at 1.70 amp, the separator’s highest current, and ferromagnetic ones as strongly attracted to a magnet, like a piece of iron. Arsenopyrite’s 3 samples had a best range above 1.70 amp. The species page, arsenopyrite, gives the same row.
- The arsenic-row count. We matched every row of USGS Table 1 to the September 2026 IMA list by script and kept those whose formula has arsenic and no oxygen: arsenides, sulpharsenides and arsenic sulphosalts. That gives 18 rows. 17 have a best range above 1.70 amp, including cobaltite, löllingite, realgar and proustite.
- Iron is not the switch. Three of the 18 have iron as a fixed part of the formula. Arsenopyrite, 34.30% iron, and löllingite, 27.15%, both stay behind. Renierite is pulled at a best range of 0.10 to 0.30 amp, and its Handbook sheet is the only one of the three that prints Magnetic. The carbonates on is siderite magnetic behave differently.
- What changes the answer: pyrrhotite. The arsenopyrite sheet lists pyrrhotite first among its associates, and USGS names pyrrhotite as ferromagnetic, best range 0.01 to 0.05 amp. A pull on an arsenopyrite specimen is information about another mineral, a magnetite inclusion or steel, not about FeAsS. Neither source tests a hand magnet.
- Toxicity is a separate question. Arsenopyrite is 46.01% arsenic by mass; that and the published guidance are on is arsenopyrite dangerous and toxic minerals in a collection. Nothing here is health, safety or legal advice.
| Mineral (USGS name) | IMA formula | Iron in formula | USGS total range (amp) | USGS best range (amp) | Samples | Class by best range (USGS definitions) |
|---|---|---|---|---|---|---|
| Arsenopyrite | FeAsS | Yes, 34.30% | 1.00 to above 1.70 | Above 1.70 | 3 | Diamagnetic |
| Loellingite (IMA: löllingite) | FeAs2 | Yes, 27.15% | Above 1.70 | Above 1.70 | 3 | Diamagnetic |
| Renierite | (Cu1+,Zn)11Fe4(Ge4+,As5+)2S16 | Yes, variable, not worked | 0.05 to 0.60 | 0.10 to 0.30 | 1 | Paramagnetic; sheet prints Magnetic |
| Cobaltite | CoAsS | No | Above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Gersdorffite | NiAsS | No | Above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Safflorite | CoAs2 | No | Above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Clinosafflorite | CoAs2 | No | 0.30 to above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Skutterudite | CoAs3 | No | Above 1.70 | Above 1.70 | 3 | Diamagnetic |
| Skutterudite-(Ni) (nearest IMA row: nickelskutterudite) | NiAs3 | No | 0.50 to above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Niccolite (IMA: nickeline) | NiAs | No | Above 1.70 | Above 1.70 | 6 | Diamagnetic |
| Domeykite | Cu3As | No | Above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Enargite | Cu3AsS4 | No | Above 1.70 | Above 1.70 | 3 | Diamagnetic |
| Tennantite (IMA: 8 tennantite-(X) rows) | Cu6(Cu4X2)As4S13 for most of the 8 | Depends on the species; tennantite-(Fe) does | 0.70 to above 1.70 | Above 1.70 | 3 | Diamagnetic |
| Colusite | Cu13VAs3S16 | No | 0.50 to above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Pearceite | [Ag9CuS4][(Ag,Cu)6(As,Sb)2S7] | No | Above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Proustite | Ag3AsS3 | No | Above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Realgar | AsS | No | Above 1.70 | Above 1.70 | 3 | Diamagnetic |
| Orpiment | As2S3 | No | Above 1.70 | Above 1.70 | 1 | Diamagnetic |
| Pyrrhotite, for scale (not counted) | Fe7S8 | Yes | Below 0.01 to 0.70 | 0.01 to 0.05 | 7 | Ferromagnetic (named by USGS) |
| Magnetite, for scale (not counted) | Fe2+Fe3+2O4 | Yes | Below 0.01 to 0.05 | 0.01 | 6 | Ferromagnetic (named by USGS) |
Is arsenopyrite magnetic? What the sheet and the separator record
Arsenopyrite is diamagnetic by its best range and has no magnetic property on its reference sheet. The Handbook of Mineralogy arsenopyrite sheet gives FeAsS, monoclinic, hardness 5.5 to 6, measured density 6.07, silver-white to steel-grey and metallic, and says nothing about magnetism. Silence on a sheet is absence from the source, not a measured zero, so the question goes to a measurement.
The measurement. USGS Open-File Report 99-529, Magnetic Susceptibilities of Minerals (Rosenblum and Brownfield) passed dry 125 to 150 µm grains through Frantz isodynamic separators at a 15 degree side tilt. Its definitions: ferromagnetic minerals are strongly attracted to a magnet, like a piece of iron, and include magnetite, maghemite, pyrrhotite and pentlandite; paramagnetic minerals are separable at up to 1.70 amp; diamagnetic minerals are nonmagnetic at 1.70 amp. Arsenopyrite, 3 samples: total range 1.00 to above 1.70 amp, best range above 1.70. The report gives no susceptibility in cgs units, so this is a class, not a number.
The boundary. Arsenopyrite is not ferromagnetic and, on its best range, not paramagnetic either. Its total range starts at 1.00 amp, and the report says of ranges running from 0.50 or 1.00 amp to above 1.70 that probably some contamination was involved; that reading is set out on the species page and is not this page’s point. USGS also writes that dark and opaque minerals are generally extracted below 1.00 amp, with many sulfides among the exceptions. Arsenopyrite is one.
Why arsenopyrite stays behind: the arsenic-row count
Method. Every data row of USGS Table 1 was parsed by script (376 of 378; the two that failed to parse, chrysolite and descloizite, carry no arsenic) and matched by name to the September 2026 IMA-CNMNC Master List (pdftotext -layout, both), and rows whose IMA formula contains arsenic and no oxygen were kept. That excludes arsenates such as scorodite. Fourteen matched automatically. Four USGS names needed a hand mapping: loellingite to löllingite, niccolite to nickeline, skutterudite-(Ni) to nickelskutterudite (our mapping), and tennantite, which the IMA list now splits into 8 tennantite-(X) rows. A raw line scan for each kept name confirmed its figures. Total: 18.
Result. 17 of the 18 have a best range above 1.70 amp: diamagnetic by the report’s definitions. They include the cobalt and nickel arsenides, the copper arsenic sulphides and sulphosalts, realgar, orpiment and proustite. The report says the same in words for three of them: niccolite, cobaltite, and skutterudite are nonmagnetic. Cobaltite, the silver-white look-alike, gives the separator nothing to pull either.
Iron is not the switch, and the documented failure is renierite. Three of the 18 have iron as a fixed part of the formula: arsenopyrite, 34.30% by mass worked; löllingite, FeAs2, 27.15%; and renierite, a copper-zinc-iron germanium sulphide with some arsenic. Tennantite may carry iron, as tennantite-(Fe), and stays behind too. The first two stay behind. Renierite is pulled at 0.10 to 0.30 amp, from one sample, and its Handbook sheet prints Magnetic. So the rule “an arsenic mineral stays behind” describes these 18 rows, with one named exception; it is not a law of arsenic, and USGS itself says chemistry is the main factor controlling susceptibility. Galena and stibnite, which also stay behind, are on is galena magnetic and is stibnite magnetic.
My arsenopyrite pulls a magnet: what changes the answer
Pyrrhotite. The arsenopyrite sheet’s association field begins pyrrhotite, pyrite, chalcopyrite, galena, gold. USGS names pyrrhotite among the ferromagnetic minerals and gives it a best range of 0.01 to 0.05 amp over 7 samples; its own Handbook sheet says magnetic, varying in intensity inversely with iron content. It is bronze-yellow to pinchbeck-brown where arsenopyrite is silver-white, hardness 3.5 to 4.5 against 5.5 to 6. A grain that pulls and looks bronze is consistent with pyrrhotite, not arsenopyrite.
Inclusions and steel. USGS notes that when micro-inclusions of magnetite or other ferromagnetic minerals are present, it is difficult or impossible to determine a mineral’s lower limit of extraction. Tool steel left by a saw or chisel is the other case; localising the response grain by grain is set out on is tetrahedrite magnetic and is not repeated here. Neither the sheet nor USGS tests a hand magnet, so this page predicts nothing about one.
Without a magnet. Colour and weight separate arsenopyrite from its brassy and silver-white look-alikes, and that is the species page’s 17-gram line, linked rather than repeated. The general magnet question is on which minerals are magnetic, with magnetite as the strongly magnetic reference. The identification guides are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.