Talc
Talc is a magnesium sheet silicate, hardness 1 and density 2.58 to 2.83. It is the only species in this site's reference set quoted at 1 with no range.
Talc is a magnesium sheet silicate, Mg3Si4O10(OH)2, with perfect {001} cleavage, a measured density of 2.58 to 2.83 and a hardness of 1. Across the 103 species sheets in this site's reference set that carry a hardness figure, talc is the only one quoted as a bare 1 with no range, because it defines the point rather than being measured against it. Most talc specimens are massive steatite rather than crystals.
In short
- Talc is hardness 1 by definition, not by measurement. Of the 103 sheets in this site's reference set that give a hardness, talc is the only one printed as a single 1 with no upper bound. Molybdenite is 1 to 1.5, graphite and aurichalcite 1 to 2. The scale is anchored on talc, so talc cannot be measured against it.
- Hardness 1 means a fingernail marks it. A fingernail sits near 2.5 on the Mohs scale, so it will mark talc, gypsum, graphite and molybdenite alike. Hardness alone does not separate talc from the other very soft species, and this is the commonest mistake made with it.
- Pyrophyllite is the species talc is actually confused with. Al2Si4O10(OH)2, hardness 1 to 2, density 2.65 to 2.90 against talc's 2.58 to 2.83, perfect {001} cleavage in both, the same greasy feel and the same platy habit. The densities overlap and no field test separates them.
- Crystals are small: the Handbook gives platy, pseudotrigonal pyramids to 1 cm. Almost every talc specimen in a collection is massive steatite, fibrous or fine-grained compact material rather than a crystal.
- The Handbook's own association list for talc names actinolite, tremolite and anthophyllite — three amphiboles that have regulated asbestiform forms. That is a fact about where talc grows, not a claim about any specimen, and questions about handling or disposal belong with the Health and Safety Executive rather than a mineral page.
| Species | Formula | Hardness | Density | What separates it from talc |
|---|---|---|---|---|
| Talc | Mg3Si4O10(OH)2 | 1 | 2.58 to 2.83 | — |
| Pyrophyllite | Al2Si4O10(OH)2 | 1 to 2 | 2.65 to 2.90 | Nothing reliable in the hand. Aluminium against magnesium, so it is a laboratory call |
| Graphite | C | 1 to 2 | 2.09 to 2.23 | Black metallic lustre; it writes on paper and talc does not |
| Molybdenite | MoS2 | 1 to 1.5 | 4.62 to 4.73 | Nearly twice the density, and a blue-grey metallic sheen |
| Gypsum | CaSO4·2H2O | 1.5 to 2 | 2.317 | Harder, and it cleaves on {010} into clear flexible plates rather than greasy scales |
| Brucite | Mg(OH)2 | 2.5 | 2.39 | Harder again; waxy rather than greasy, and it is a hydroxide, not a silicate |
| Vermiculite | (Mg,Fe,Al)3(Si,Al)4O10(OH)2·4H2O | About 1.5 | 2.2 to 2.6 | It expands dramatically on heating; talc does not |
Why talc has one hardness number and everything else has a range
Open any species sheet in this site's reference set and the hardness is nearly always a span: quartz 7, variable by direction; marcasite 6 to 6.5; magnesite 3.5 to 4.5. Talc is printed as 1. No range, no qualifier.
That is not because talc has been measured more carefully than anything else. It is because the Mohs scale is an ordinal scale defined by ten reference minerals, and talc is the first of them. Asking how hard talc is on the Mohs scale is asking how talc compares with talc.
Counted across the 103 sheets in the reference set that record a hardness at all, seven species have a minimum below 2 — talc, molybdenite, graphite, aurichalcite, covellite, gypsum and realgar — and talc is the only one of the seven with no upper bound printed. Molybdenite is 1 to 1.5; graphite and aurichalcite 1 to 2; covellite, gypsum and realgar 1.5 to 2.
The practical consequence is narrow and worth holding on to: a scratch test tells you a specimen is very soft, and it stops there. It cannot tell you the specimen is talc. For the method and its limits, see how to test mineral hardness properly.
Talc and pyrophyllite are the same shape, the same feel and the same hardness
Pyrophyllite, Al2Si4O10(OH)2, is talc with aluminium where the magnesium sits. The consequences are almost nil at the level a collector can test.
Both are monoclinic or triclinic sheet silicates. Both cleave perfectly on {001}. Both are sectile, flexible and inelastic. Both feel greasy. The Handbook of Mineralogy gives pyrophyllite a hardness of 1 to 2 against talc's 1, and a density of 2.65 to 2.90 against 2.58 to 2.83 — the density ranges overlap over almost their whole width.
So the honest position is that a hand specimen labelled talc that came out of a pyrophyllite deposit cannot be checked at home, and the reverse is equally true. If it matters — and for a locality-complete suite it does — the determination is an X-ray or chemical one. A label that says talc with no locality and no analysis is a guess, which is the argument made at greater length on whether a specimen without a locality is worth buying.
The company talc keeps, and what that does and does not mean
The Handbook of Mineralogy lists talc's associated species as actinolite, tremolite, chlorite, pyroxene, vermiculite, serpentine, anthophyllite, dolomite and calcite. Three of those — actinolite, tremolite and anthophyllite — are amphiboles with regulated asbestiform forms.
That association is a statement about geology. Talc forms by hydrothermal alteration of mafic rocks following serpentinisation, and by low-temperature metamorphism of siliceous dolostones; the amphiboles form in the same rocks under the same conditions, which is why they turn up on the same shelf of a quarry.
It is not a statement about any particular specimen, and this page deliberately does not make one. A massive steatite block from a metamorphosed dolostone and a fibrous seam from an ultramafic body are different material with different histories. Anything to do with handling, cutting, dust or disposal is a matter for the Health and Safety Executive and, in a museum context, a conservator — not for a mineral reference page.
One narrow, checkable thing is worth recording. The archived product list of the mineral business previously at this domain includes a specimen catalogued as actinolite in talc. We are not that business, we hold none of that stock and no description of theirs is reproduced here; the list is used only as a snapshot of what a real dealer's inventory contained. What it shows is that the association is not theoretical — it reaches the specimen shelf.
Where talc crystals actually come from
Talc is worked industrially in enormous quantity and collected in very small quantity, and the two sets of localities barely overlap. The Handbook singles out Mt Greiner in the Zillertal, Tirol; Zermatt in Valais and St Gotthard in Ticino; the Pfitschtal in Trentino-Alto Adige; the Trimouns deposit six kilometres north-east of Luzenac in the Ariège; Goepfersgruen in Bavaria; Snarum in Norway; and the Onotosk deposit in Irkutsk, Siberia.
In the United States: Fowler in St Lawrence County, New York; Delta in York County, Pennsylvania; Smithfield, Rhode Island; Rochester, Vermont; Holly Springs, Georgia; and near San Andreas in Calaveras County, California.
The name is probably from the Arabic talq. Against the eleven United Kingdom type localities among the species on this site — set out on the pharmacosiderite page — talc has no recorded country of first description at all: the IMA-CNMNC Master List gives its status as grandfathered, its country as unknown and its original reference as a 1546 reprint.
We do not sell specimens and there is no catalogue here. If you are looking for crystallised talc from a named locality, the route is the wanted list, and the rest of this section of the site is indexed under mineral species.