Is sylvite a halide?
Yes. Sylvite, KCl, is a halide mineral: potassium chloride, 47.55% chlorine. Halide names the class, halite one species. Telling a sylvite crystal from halite.
Yes. Sylvite is potassium chloride, KCl, and a halide: webmineral puts it in the halide class, Strunz 03.AA.20, with halite. Worked, it is 47.55% chlorine by mass against halite’s 60.66%. Halide is the class and halite one species, NaCl; sylvite, hardness 2 and density 1.993, is a halide but not halite.
In short
- The definition. Webmineral classifies sylvite in Strunz class 03, halides (03.AA.20, simple halides without H2O), and Dana class 09, anhydrous and hydrated halides, in the same groups as halite. The September 2026 IMA-CNMNC Master List lists it as KCl, status G, 1832; the list has no class column, and a scan finds 0 lines containing halide.
- Halide or halite: the class-and-species rule. A halide is a class; halite is one species, sodium chloride, NaCl. Sylvite is a halide and not halite; carnallite, KMgCl3·6H2O, is a halide too, in Strunz 03.BA, simple halides with water. Witherite, a carbonate, is Strunz class 05 on the same database.
- The one-to-one chlorides, by script. Of the IMA rows whose formula is one cation and chlorine alone, a script finds 13; 6 are 1:1, MCl: calomel, chlorargyrite, halite, lafossaite, nantokite and sylvite. Two carry an alkali metal: halite and sylvite. Two independent scans of the list agree.
- The chloride ledger, worked. Chlorine per 100 g: halite 60.66 g, sylvite 47.55 g, carnallite 38.28 g, chlorargyrite 24.74 g. Potassium is heavier than sodium, so sylvite carries 13.11 g less chlorine per 100 g than halite with the same one-to-one formula.
- Where the tests fail, documented. Sylvite and halite are both cubic with perfect {001} cleavage and both colourless to white, so neither cleavage nor colour separates them. Both sheets say soluble in H2O, so the in-water weighing used elsewhere does not work. Density, 1.993 against 2.168, and index, 1.4903 against 1.5443, do.
| Name | IMA row (formula, status) | Class (webmineral, Strunz) | Chlorine by mass, worked | Hardness | Density | Refractive index | In water (sheet) |
|---|---|---|---|---|---|---|---|
| Sylvite | KCl, G, 1832 | 03.AA.20 halides | 47.55% | 2 | 1.993 | n 1.4903 | Soluble |
| Halite | NaCl, G, 1847 | 03.AA.20 halides | 60.66% | 2 to 2.5 | 2.168 | n 1.5443 | Soluble; rarely fluoresces red under SW UV |
| Carnallite | KMgCl3·6H2O, G, 1856 | 03.BA.10 halides with H2O | 38.28% | 2.5 | 1.602 | α 1.465 to γ 1.496 | Soluble; deliquescent in high humidity, then dissolving |
| Chlorargyrite | AgCl, A, 1962 s.p. | Not fetched | 24.74% | 2.5 | 5.556 | n 2.071 | Not printed |
| Sylvinite | No row (0 lines contain sylvin) | - | Depends on the mix | - | - | - | Potassium chloride and halite (USGS) |
| Potash | No row (0 lines contain potash) | - | - | - | - | - | Salts with water-soluble potassium (USGS) |
Is sylvite a halide? The definition in one sentence
Sylvite is a halide: potassium chloride, KCl, a compound of a metal with chlorine and nothing else. Webmineral’s sylvite page gives its Dana class as 09, anhydrous and hydrated halides (09.01.01.02), and its Strunz class as 03, halides, subdivision 03.A, simple halides without H2O (03.AA.20). Halite sits in the same Dana group, 09.01.01.01, and the same Strunz group, 03.AA.20.
The IMA test, by script. The September 2026 IMA-CNMNC Master List has a sylvite row: KCl, status G, 1832, Italy. The list records names, formulas and status, not classes; a case-insensitive scan finds 0 lines containing halide. The classification comes from the systems above, and the species from the list. The Handbook sylvite sheet gives KCl too, typically nearly pure.
What the species page adds. Hardness 2, density 1.993, cubic crystals to 15 cm, perfect {001} cleavage, isotropic with n = 1.4903. Sylvite’s potash ledger and the USGS table slip are on sylvite and are not repeated here.
Halide or halite? The class-and-species rule
The class-and-species rule: halide names a class of minerals, halite names one species in it, so sylvite is a halide and is not halite. Halite is sodium chloride, NaCl on the IMA list and on its Handbook sheet. USGS Open-File Report 2016-1167 says halite is also known as sodium chloride or common salt, and calls sylvite potassium chloride in natural mineral form.
Other halides on the same beds. Carnallite, KMgCl3·6H2O, is a halide with water: webmineral puts it in Strunz 03.BA.10, simple halides with H2O, and Dana 11, halide complexes. chlorargyrite, AgCl, is a halide of silver. Both are chlorides; neither is halite.
What is not a halide. On the same database witherite, BaCO3, is Strunz class 05, carbonates, and the tungstates ferberite and hübnerite are 04, oxides. An evaporite specimen can carry anhydrite or gypsum beside sylvite; those are sulphates, and the label should say which crystal is which.
The one-to-one chlorides: 6 rows, 2 alkali metals
A script over the IMA list finds 13 rows whose formula is one cation and chlorine alone; 6 of them are one-to-one, MCl, and 2 of those carry an alkali metal: halite and sylvite. Method: the September 2026 list was converted with pdftotext -layout and each line parsed into name, formula and status, 6,114 pairs of the 6,239 species the list says it holds; formulas matching a single element symbol, optional valence, then Cl and an optional count were kept. A second scan, of the first three tokens on every line, returns the same 13.
The 13. One-to-one: calomel HgCl, chlorargyrite AgCl, halite NaCl, lafossaite TlCl, nantokite CuCl and sylvite KCl. Two-to-one and three-to-one: chloromagnesite MgCl2 (status Q, questionable), cotunnite PbCl2, lawrencite FeCl2, scacchite MnCl2, tolbachite CuCl2, vegrandisite BaCl2 and molysite FeCl3.
The chloride ledger, worked. Chlorine by mass is 60.66% in NaCl, 47.55% in KCl, 38.28% in KMgCl3·6H2O and 24.74% in AgCl. The heavier the cation, the less chlorine per gram: sylvite carries 13.11 g less per 100 g than halite on the same formula type. The halite sheet’s Cardona, Spain analysis prints 60.27% Cl against its 60.66 ideal.
Sylvite or halite? What separates them, and what does not
Density and refractive index separate sylvite from halite; cleavage, habit and colour do not. On their sheets sylvite reads hardness 2, density 1.993 and n 1.4903; halite reads 2 to 2.5, 2.168 and 1.5443. Halite is 8.8% denser and 0.054 higher in index, and both are isotropic, so each gives a single refractometer reading.
Documented failures. Both sheets give cubic crystals and perfect {001} cleavage, so a cleavage cube is either. Both are colourless to white, and the sylvite sheet prints yellowish red to red when included with hematite, so colour does not decide either. Both sheets say soluble in H2O: the in-water weighing on how to measure specific gravity at home would dissolve the specimen while measuring it, and this page gives no substitute recipe. The halite sheet records rare red fluorescence under shortwave UV; the sylvite sheet records none.
Not covered. This page gives no handling guidance; hazard questions route to toxic minerals in a collection, which is not advice. The halite page’s humidity table is not repeated here.
When the answer changes: sylvinite, potash and carnallite
A label reading sylvinite or potash is not a species name, and the halide answer then applies to the parts, not the whole. USGS describes sylvinite as potassium chloride and halite, a mixture of two halides, and a scan of the IMA list finds 0 lines containing sylvin. USGS Mineral Commodity Summaries 2025, Potash uses potash for mined and manufactured salts containing water-soluble potassium, a commodity word; 0 IMA lines contain potash.
Carnallite is the potassium halide that is not sylvite. KMgCl3·6H2O is a halide with water, orthorhombic, density 1.602 and biaxial (+), α 1.465 to γ 1.496, against sylvite’s isotropic 1.4903. Its sheet prints deliquescent in high humidity, then dissolving; the sylvite sheet prints only soluble in H2O. Both sheets list the other as an associate.
Magnetism does not help. USGS Open-File Report 99-529 left sylvite, 1 sample, and halite, 2 samples, unpulled at 1.70 amp. The classification questions are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.