Key properties
| Chemical formula | FeS2 |
| Crystal system | Cubic (isometric) |
| Mohs hardness | 6-6.5 |
| Toughness | Fair to good (brittle) |
| Optic character | Isotropic; opaque with metallic reflectivity — RI far above refractometer limits |
| Specific gravity | 4.80-5.20 |
| Cleavage | None (indistinct cubic parting sometimes seen) |
| Fracture | Conchoidal to uneven; brittle |
| Habit | Cubes and pyritohedra with characteristic striated faces; also massive, granular, reniform and radiating 'pyrite suns' |
| Lustre | Splendent metallic; polish: Bright metallic |
| UV fluorescence | Inert |
| Pleochroism | None |
| Cause of colour | Brass-yellow is intrinsic to the iron sulfide electronic structure (a natural semiconductor's band absorption and high reflectivity) — not a trace-element chromophore |
| Typical inclusions | Frequently intergrown with marcasite, chalcopyrite or sphalerite; growth striations on crystal faces |
| Stability | Tarnishes to iridescent or dull brown films in humid or chemically active environments; decomposes on geological timescales; soluble in nitric acid |
| Heat sensitivity | Fuses easily under a jeweller's torch; can become weakly magnetic after heating |
| Care and cleaning | Warm soapy water and prompt thorough drying; avoid ultrasonic and steam where possible, and definitely avoid heat, acids and prolonged humidity |
| Birthstones | None |
| Availability | Plentiful as crystal specimens and drusy plates; limited as calibrated faceted stones |
| Recognition | Brassy metallic yellow, greenish-black streak, hardness 6-6.5 (scratches glass), distinctly heavy in the hand (SG ~5), non-magnetic unless heated, no RI readable |
Varieties
Pyrite
| Colour | brassy to pale golden metallic yellow |
| Transparency | opaque |
| Clarity type | Not applicable — opaque |
| Phenomena | None (iridescent tarnish films occasionally add rainbow flashes) |
| Appearance | Bright, brassy, mirror-reflective yellow metal; faceted stones flash like foil; natural cube crystals and drusy encrustations are set whole into silver; older pieces may show dull brown or iridescent tarnish |
| Trade names | Marcasite (jewellery trade usage — almost always pyrite) • pyrite drusy • 'fool's gold' |
| Misnomers | Marcasite (trade name for pyrite in antique and fashion jewellery — true marcasite is orthorhombic FeS2 and deteriorates) • fool's gold (gold rush nickname) |
| Typical sizes | Faceted rose cuts usually a few millimetres (small calibrated sizes); crystal specimens and drusy plates from a few carats to kilos |
| Cutting styles | Small faceted rose cuts and flat tables set pavilion-up • bead-carved spheres • whole crystal clusters and drusy slabs in silver |
| Key separations | vs chalcopyrite: chalcopyrite tarnishes to iridescent colours more quickly and is softer (3.5-4); pyrite harder and stays brassy • vs gold: gold is malleable, sectile and leaves a yellow streak; pyrite is brittle, crushes to powder and streaks greenish-black • vs hematite: hematite is grey-black with a red-brown streak; pyrite streaks greenish-black • vs marcasite mineral: both brassy, but marcasite is orthorhombic with spear-shaped crystals and decomposes — gem lab ID needs XRD or careful morphology |
| Sources (localities) | Peru (Huanzali, Huarón and other Ancash mines — main faceted/druse supply) • Spain (Navajún, La Rioja — world-famous sharp cubes; historic Rio Tinto) • Bulgaria (Madan ore field) • Mexico • Italy • USA |
| Availability | Plentiful as specimens and drusy material; faceted 'marcasite' cuts always available in commercial volume |
| Market notes | Essentially a decorative silver-jewellery stone; priced per piece or per strand, rarely per carat; antique 'marcasite' jewellery carries vintage premium regardless of the stone |
| Care notes | Wear with care — facets chip and settings loosen with knocks; store dry; remove before sports, swimming and housework; a soft dry cloth restores brightness |
| In short | Pyrite delivers metallic glitter at minimal cost, either as tiny rose cuts in 'marcasite' jewellery or as whole crystal clusters. Its brittleness and tarnish susceptibility define its care regime, and its streak instantly separates it from gold and hematite. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.10–3.00 | $0.30 – $2.00 | commercial faceted rose cuts | 2026-10-26 |
| 1.00–500.00 | $0.10 – $1.00 | drusy plates, beads and carvings | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #195
Related materials: Corundum · Diamond · Opal · Quartz · Spinel · Topaz
Identification wizard · All 83 materials · Singapore gem labs