How to tell if pyrite is real
A real pyrite specimen is a brass-yellow sulphide, hardness 6 to 6.5, streak greenish black. A solid 8 mm pyrite bead weighs 1.345 g; glass, under 1.21 g.
To tell if pyrite is real, check in order: brass-yellow colour with cubic or striated crystals, a greenish-black streak, hardness 6 to 6.5 on its Handbook sheet, and, for beads, mass. A solid 8 mm pyrite bead weighs 1.345 g; the same bead in glass, 0.617 to 1.206 g. Real pyrite contains no gold in its sheet analyses.
In short
- Real means two things here: the mineral and the object. Pyrite the mineral is FeS2, cubic, hardness 6 to 6.5 and density 5.018 on its Handbook of Mineralogy sheet. The object can be the mineral, a look-alike mineral, or an imitation. A stone labelled marcasite in jewellery is, says the International Gem Society, frequently pyrite.
- Fool's gold is three minerals, not one. The USGS names pyrite as the commonest, then chalcopyrite and weathered mica. Pyrite and chalcopyrite flake, powder or crumble when poked with a metal point, where gold gouges like soft lead. Pyrite and chalcopyrite streak dark green to black, gold golden yellow, the micas white.
- The 4.6 line, for beads: divide one bead's mass by its volume, πd³/6. A drilled 8 mm pyrite bead works out at 4.90 and marcasite at 4.77. Glass, at most 4.50 on the gem society's figures, works out at no more than 4.39, and chalcopyrite at 4.20. At 4.6 or above the bead is behaving as iron sulphide; well below it, it is not solid pyrite.
- Rainbow colours do not make pyrite fake. The Handbook sheet says pyrite tarnishes darker and iridescent, and the IGS describes it as brassy yellow, sometimes with iridescent tarnish. The streak, not the surface colour, is the test.
- Real pyrite is not gold-bearing by definition. The three analyses on the pyrite sheet report iron, sulphur, nickel, cobalt and silica, and no gold. The golden flecks in lapis lazuli are pyrite, in GIA's description, not gold.
| What it could be | Source | Hardness | Streak | Solid 8 mm round bead | Drilled bead, mass ÷ volume | What decides it |
|---|---|---|---|---|---|---|
| Pyrite, FeS2 | Handbook sheet | 6 to 6.5 | Greenish black to brownish black | 1.345 g | 4.90 | Streak and crystal form; for beads, 4.6 or above |
| Marcasite-set jewellery stones | IGS: frequently pyrite | As pyrite, if pyrite | As pyrite, if pyrite | 1.345 g, if pyrite | 4.90, if pyrite | A trade name, not a species determination |
| Marcasite, the species, FeS2 | Handbook sheet | 6 to 6.5 | Greyish or brownish black | 1.310 g | 4.77 | Habit; 2.6% lighter than pyrite, not a home test |
| Chalcopyrite, CuFeS2 | Handbook sheet; USGS | 3.5 to 4 | Greenish black | 1.099 to 1.153 g | 4.00 to 4.20 | Hardness: at least 2 Mohs steps below pyrite |
| Gold, Au | Handbook sheet; USGS streak | 2.5 to 3 | Golden yellow (USGS) | 5.174 g | 18.85 | Dents rather than powders; 3.85 times the mass |
| Weathered mica (muscovite) | USGS; Handbook muscovite sheet | 2.5 to 4, by direction | White | Not made as beads | Not applicable | Flexible, elastic flakes |
| Glass imitation | IGS glass article: SG 2.30 to 4.50 | Not given | Not given | 0.617 to 1.206 g | 2.25 to 4.39 | Below the 4.6 line |
How to tell if pyrite is real: five checks, in order
Start with a lens and a white tile, and finish, if you need to, at a laboratory. The order runs from harmless to destructive. The Handbook of Mineralogy pyrite sheet supplies the numbers: FeS2, cubic, hardness 6 to 6.5, density 5.018, streak greenish black to brownish black. Day one needs a 10x lens, a piece of unglazed porcelain and, for beads, a scale reading to 0.01 g and a caliper.
- Form. Look for cubes, pyritohedra or octahedra; the sheet records striations conforming to pyritohedral symmetry. Crystal form is the cheapest evidence a piece offers.
- Colour on a fresh surface. The sheet gives pale brass-yellow, tarnishing darker and iridescent. A silver-white piece is a different question, covered on why is my pyrite silver.
- Streak, on rough only. Pyrite leaves a dark streak; gold leaves golden yellow. The technique is on how to use a streak plate. A streak scars a polished bead, so for beads skip to step 5.
- Hardness, on rough only. Pyrite, 6 to 6.5, is at least two Mohs steps harder than chalcopyrite, 3.5 to 4, and gold, 2.5 to 3. Method: how to test mineral hardness properly.
- Bead mass. Apply the 4.6 line, below.
The finish state is one of four labels: pyrite; iron sulphide, pyrite or marcasite undecided; another mineral, usually chalcopyrite; or an imitation. The species page, pyrite, sets out its own three-step rule against gold, which this page does not repeat. The identification guides are indexed at the collecting guides.
Is my pyrite bracelet real? The 4.6 line for beads
The 4.6 line: a bead's mass divided by its volume, πd³/6, of 4.6 or more points to iron sulphide; well below it, the bead is not solid pyrite. Strung beads cannot be weighed in water one at a time, but they can be weighed and measured. An 8.0 mm sphere is 0.2681 cm³. At pyrite's 5.018 a solid bead is 1.345 g; a 1 mm drill hole removes 2.3% of the volume, so a drilled bead works out at 4.90. Marcasite, 4.887, gives 4.77.
Worked example. Twenty 8.0 mm beads off the string weigh 26.2 g: 1.310 g a bead, 4.89 by the formula, which fits pyrite. Twenty that weigh 15.0 g give 0.750 g a bead and 2.80, which fits neither pyrite nor marcasite. The International Gem Society glass article gives glass a specific gravity of 2.30 to 4.50, so even the heaviest glass works out at no more than 4.39 drilled; chalcopyrite, 4.1 to 4.3, at no more than 4.20.
Where the line needs care. A 0.1 mm error in an 8 mm diameter is a 3.8% error in volume, so measure several beads with a caliper and average them, and weigh beads without the cord or clasp. Readings within about 0.2 of the line, 4.4 to 4.8, should be re-measured before they are trusted. The line cannot separate pyrite from marcasite, and it cannot see a coating. For loose pieces, the in-water method on how to measure specific gravity at home is better. This page gives no buying advice.
Is it pyrite, gold, chalcopyrite or mica?
The USGS names three minerals as fool's gold: pyrite, the commonest, chalcopyrite and weathered mica. Its test is a metal point and a streak. Pyrite and chalcopyrite flake, powder or crumble; gold gouges or indents like soft lead. On porcelain, gold leaves a golden yellow streak, pyrite and chalcopyrite dark green to black, and the micas white.
Chalcopyrite matches pyrite on colour and streak. Its Handbook sheet gives CuFeS2, brass-yellow, may be tarnished and iridescent, with a greenish-black streak, so colour and streak do not separate the two. Hardness does: 3.5 to 4 against 6 to 6.5. Its tetrahedral-looking crystals are on chalcopyrite and is chalcopyrite the same as peacock ore.
Mica gives itself away by splitting. The Handbook muscovite sheet records laminae that are flexible and elastic, and a white streak. Gold's full comparison, with the cube arithmetic, is on what is fool's gold.
Marcasite jewellery, rainbow tarnish and gold flecks: labels that mislead
Marcasite jewellery is usually pyrite under a trade name. The International Gem Society pyrite article says stones sold as marcasite are frequently pyrite, since pyrite is the more stable. The gem society's marcasite article adds that steel imitations of this jewellery exist. The species difference is on is marcasite the same as pyrite.
Iridescent pyrite can be natural. The sheet itself records an iridescent tarnish. Whether a particular rainbow surface is tarnish or an applied coating is a question for the general checks on how to tell if a crystal is fake; this page makes no claim about coated pyrite products. Crumbling or cracking is decay, not fakery: see why is my pyrite crumbling.
Gold in pyrite. None of the sheet's analyses reports gold. In lapis lazuli the golden flecks are pyrite, as GIA describes them; the rock is covered on is lapis lazuli a mineral or a rock. Nothing on this site is offered for sale; the wanted list is the only commercial route.