Millerite
Millerite, NiS, grows brass-yellow capillary crystals to 7 cm: hexagonal, hardness 3 to 3.5, density 5.5, streak greenish black. It is 64.67% nickel by mass.
Millerite is nickel sulfide, NiS on the IMA list (G, 1845): a hexagonal mineral of pale brass-yellow capillary crystals to 7 cm, hardness 3 to 3.5, density 5.5, streak greenish black. Ideal NiS is 64.67% nickel by mass. A 20.00 g cleavable piece reads 16.36 g in water, heavier than pyrite, marcasite, chalcopyrite, pentlandite or pyrrhotite.
In short
- The species. The Handbook of Mineralogy sheet gives NiS, hexagonal, as slender to capillary crystals to 7 cm in radiating groups of hairlike, interwoven masses, single crystals sometimes helically twisted or formed into rings, hardness 3 to 3.5, density 5.5, pale brass-yellow tarnishing to iridescence, streak greenish black. The September 2026 IMA-CNMNC Master List gives NiS, status G, 1845.
- The nickel–sulfur ladder. A field scan of the IMA list, checked by a token scan, finds 4 rows made of nickel and sulfur alone. Worked on standard atomic weights: heazlewoodite Ni3S2 73.31% nickel, density 5.82; millerite NiS 64.67%, 5.5; polydymite Ni3S4 57.86%, 4.5 to 4.8; vaesite NiS2 47.79%, 4.45. More sulfur per nickel, less nickel and a lighter piece, down the whole ladder.
- Worked on the sheet: Marbridge. The sheet’s Marbridge mine analysis, Quebec, has 63.68 wt% Ni, 1.03 Fe, 0.21 Co and 35.47 S. Converted to atoms, metals and sulfur stand at 1.001 to 1, and nickel holds 98.0% of the metal atoms, matching the sheet’s (Ni0.98Fe0.02)S1.00. The nickel is 98.5% of the ideal 64.67.
- The brass-needle check. A 20.00 g piece reads 16.36 g in water as millerite; pyrite 16.01 g, pentlandite 15.65 to 16.00, marcasite 15.91, pyrrhotite 15.63 to 15.70 and chalcopyrite 15.12 to 15.35. Pyrite and marcasite are hardness 6 to 6.5 against millerite’s 3 to 3.5. Documented failure: chalcopyrite’s streak, greenish black, is the same as millerite’s.
- Type locality, two answers. The Handbook marks Germany [TL], naming Müsen, Wissen and Ramsbeck; the September 2026 IMA list gives Czech Republic as the country of first description. Both are printed here; neither is corrected. The sheet names the mineral for William Hallowes Miller (1801–1880), who first studied its crystals.
| Name | Formula (IMA), status | System (sheet) | Habit (sheet) | Hardness | Density | 20.00 g piece in water | Ni by mass | Streak (sheet) | Colour (sheet) |
|---|---|---|---|---|---|---|---|---|---|
| Millerite | NiS; G, 1845 | Hexagonal | Slender to capillary crystals to 7 cm, radiating hairlike masses | 3–3.5 | 5.5 | 16.36 g | 64.67% | Greenish black | Pale brass-yellow to bronze-yellow |
| Heazlewoodite | Ni3S2; G, 1897 | Hexagonal | Massive, fine-grained; rarely minute crystals | 4 | 5.82 | 16.56 g | 73.31% | n.p. | Pale bronze |
| Polydymite | Ni2+Ni3+2S4; G, 1876 | Cubic | Dominantly octahedral crystals | 4.5–5.5 | 4.5–4.8 | 15.56–15.83 g | 57.86% | n.p. | Pale gray to steel-gray |
| Vaesite | NiS2; G, 1945 | Cubic | Octahedra and cubes to 1 cm; massive | About 3.5 | 4.45 | 15.51 g | 47.79% | n.p. | Black |
| Pentlandite | (Ni,Fe)9S8; G, 1856 | Cubic | Massive, granular; rarely crystals | 3.5–4 | 4.6–5.0 | 15.65–16.00 g | Variable | Pale bronze-brown | Pale bronze-yellow |
| Pyrrhotite | Fe7S8; G, 1835 | Monoclinic, pseudohexagonal | Tabular or platy crystals; massive, granular | 3.5–4.5 | 4.58–4.65 | 15.63–15.70 g | 0% | Dark grayish black | Bronze-yellow to pinchbeck-brown |
| Chalcopyrite | CuFeS2; G, 1725 ? | Tetragonal | Tetrahedral-shaped crystals; massive | 3.5–4 | 4.1–4.3 | 15.12–15.35 g | 0% | Greenish black | Brass-yellow |
| Pyrite | FeS2; G | Cubic | Cubic, pyritohedral, octahedral; may be elongated to acicular | 6–6.5 | 5.018 | 16.01 g | 0% | Greenish black to brownish black | Pale brass-yellow |
| Marcasite | FeS2; G, 1845 | Orthorhombic | Tabular, pyramidal, prismatic and, rarely, capillary | 6–6.5 | 4.887 | 15.91 g | 0% | Grayish or brownish black | Tin-white, pale bronze-yellow |
What is millerite? Nickel sulfide in hairlike crystals
Millerite is nickel sulfide, NiS, best known as sprays of brass-yellow capillary crystals. The Handbook of Mineralogy millerite sheet gives hexagonal, point group −3 2/m, space group R−3m, typically as slender to capillary crystals to 7 cm, elongated along [0001], in radiating groups of hairlike, interwoven masses and columnar tufted coatings. Single crystals may be helically twisted about [0001] or form rings; it also occurs as cleavable masses up to several cm across. It cleaves perfectly on {10-11} and {01-12}, twins by pressure on {01-12}, and is brittle, though the capillary crystals are elastic. Hardness 3 to 3.5, Vickers 179, measured density 5.5 against a calculated 5.374.
Colour and optics. Pale brass-yellow to bronze-yellow, tarnishing to iridescence; streak greenish black; lustre metallic; opaque, strongly anisotropic. The sheet prints no magnetic property; what USGS measured, and did not measure, is on is millerite magnetic. Hair-like sprays such as millerite are the class that how to pack and ship mineral specimens singles out as where most transit damage happens.
Occurrence. The sheet says most commonly a low-temperature mineral, in cavities in limestones and carbonate veins and in barite; an alteration product of other nickel minerals; also in sedimentary rocks associated with coal measures, and rarely in serpentines. Its associates: gersdorffite, polydymite, nickeline, galena, sphalerite, pyrite, chalcopyrite, pyrrhotite, pentlandite, cubanite, calcite, dolomite, siderite, barite and ankerite.
How much nickel is in millerite? The nickel–sulfur ladder
Ideal millerite is 64.67% nickel by mass, the second rung of a four-rung ladder. A field scan of the September 2026 IMA list, splitting each line on runs of two or more spaces and checked by a token scan, finds exactly 4 rows whose formula contains nickel and sulfur and nothing else, and 1 row written exactly NiS: millerite. Worked on standard atomic weights (Ni 58.693, S 32.06): heazlewoodite, Ni3S2, 73.31% nickel; millerite, NiS, 64.67%; polydymite, Ni2+Ni3+2S4, 57.86%; vaesite, NiS2, 47.79%. The sheet’s own ideal column prints 64.67 Ni and 35.33 S.
The ladder in the hand. On the four sheets, density falls as sulfur rises: heazlewoodite 5.82, millerite 5.5, polydymite 4.5 to 4.8, vaesite 4.45. A 20.00 g piece reads 16.56, 16.36, 15.56 to 15.83 and 15.51 g in water. Only millerite is described with capillary crystals; heazlewoodite is massive and fine-grained, polydymite dominantly octahedral, vaesite in octahedra and cubes to 1 cm.
Worked on the sheet’s analysis. The Marbridge mine analysis, Malartic, Quebec, by electron microprobe, has 63.68 wt% Ni, 1.03 Fe, 0.21 Co and 35.47 S. Divided by atomic weights, the metals and sulfur stand at 1.001 to 1, nickel holds 98.0% of the metal atoms, iron 1.7% and cobalt 0.3%, which is the sheet’s (Ni0.98Fe0.02)Σ=1.00S1.00. Its nickel is 98.5% of the ideal 64.67. Substitute any analysis in the same way. This page makes no claim about millerite as a nickel ore: no USGS or BGS source fetched for it says so.
Millerite or pyrite? The brass-needle check
Hardness and weight separate millerite from the other brass-yellow sulfides; streak does not. Pyrite and marcasite are hardness 6 to 6.5 on their sheets, against millerite’s 3 to 3.5, and the sheets do not rule them out by habit: pyrite may be elongated to acicular, and marcasite is, rarely, capillary. At the measured densities a 20.00 g piece reads 16.36 g in water as millerite, 0.35 g more than pyrite’s 16.01 g and 0.46 g more than marcasite’s 15.91 g. Pentlandite, 15.65 to 16.00 g, comes within 0.36 g, pyrrhotite within 0.66 g, chalcopyrite no closer than 1.01 g. The pyrite family is set out on pyrite and what is fool’s gold.
Documented failure: the streak. The millerite sheet gives a greenish black streak; the chalcopyrite sheet gives greenish black too, and the pyrite sheet greenish black to brownish black. Three brass-yellow sulfides, one streak colour. Chalcopyrite is separated by its tetrahedral-shaped crystals and by weight, 15.12 to 15.35 g against 16.36 g. The methods are on how to use a streak plate, how to test mineral hardness properly and how to measure specific gravity at home.
Documented failure: the balance and a hair spray. The in-water figures assume a solid, matrix-free piece. A spray of capillary crystals on calcite or in a geode cannot be weighed that way; the sheet’s cleavable masses, up to several cm, can. For a spray, habit, colour and the hardness of a crystal tip are what is left.
Where millerite is found, and the type-locality disagreement
The Distribution field opens numerous localities worldwide. In Germany [TL], Müsen and Wissen, with large crystals at Ramsbeck, North Rhine-Westphalia, and Kamsdorf, Thuringia; large cleavages at Kotalahti, Finland; Kladno, Czech Republic; Merthyr Tudful, Glamorgan, Wales. In the USA, the Sterling mine, Antwerp, New York, and the Gap Nickel mine, Pennsylvania; in geodes at Keokuk, Iowa, St. Louis, Missouri, Esterbrook Park, Milwaukee, Wisconsin, and Hall’s Gap, Kentucky. In Canada, Temagami, Ontario, the Thompson mine, Manitoba, the Orford nickel mine and, for large cleavages, the Marbridge mine, Quebec. Also Kambalda and the Agnew mine, Western Australia; the Trojan nickel mine, Bindura, Zimbabwe; and Mabilikwe Hill, South Africa.
Two answers to one question. The Handbook marks Germany as the type locality. The September 2026 IMA list gives the Czech Republic as the country in which millerite was first discovered, with a first reference to Haidinger’s Handbuch der Bestimmenden Mineralogie (1845). The sheet also lists Kladno, Czech Republic, among its localities. This page does not choose between them.
Its neighbours. pyrrhotite and pentlandite share its rocks and its association list; chalcopyrite and pyrite share its colour; marcasite is the other brass-coloured iron sulfide in the table above. The rest is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.