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Alunite
Alunite is sulfate (alunite supergroup), KAl₃(SO₄)₂(OH)₆. In the hand, it rates 3.5 to 4 on the Mohs scale, and it runs white and gray. Dense-looking but unremarkable pale massive mineral from steamy altered volcanic ground, identified mostly by its acid-altered rock neighborhood and no fizz.
The geology.
Alunite carries the formula KAl₃(SO₄)₂(OH)₆. It belongs to the trigonal system. Catalogues list it as sulfate (alunite supergroup).
It sits at 3.5 to 4 on the Mohs scale. The surface reads vitreous to pearly; massive form dull. Light behaviour is translucent to opaque. Specific gravity runs 2.6 to 2.8. The streak is white. It breaks with distinct basal cleavage; uneven to splintery fracture.
Dense-looking but unremarkable pale massive mineral from steamy altered volcanic ground, identified mostly by its acid-altered rock neighborhood and no fizz.
It reaches buyers as massive fine-grained chunks, veins in altered volcanic rock or rare small rhombs.
The origins.
Acid-altered volcanic zones; notable: Tolfa (Italy), Spain, Utah (USA, Marysvale), Australia.
On value, the database notes: inexpensive; mainly of field-collector interest.
Traditional associations.
In energy work traditions, alunite has little established lore; it is sometimes carried as a 'stabilizing' stone by collectors.
We keep this section because people ask. It sits below the geology on purpose, and none of it describes something the stone does.
Spotting the real thing.
Dense-looking but unremarkable pale massive mineral from steamy altered volcanic ground, identified mostly by its acid-altered rock neighborhood and no fizz.
| Looks like | How to tell them apart |
|---|---|
| Limestone/calcite | Calcite fizzes in vinegar; alunite never does |
| Magnesite | Very similar in hand, magnesite fizzes in warm acid; alunite stays inert |
| Howlite | Howlite shows gray web veins |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on alunite.
| Test | What you should see |
|---|---|
| Acid check | No fizz even in warm vinegar |
| Scratch check | Knife scratches it |
| By eye | Often associated with bleached, sulfur-stained volcanic rock |
Stop short of anything that leaves a mark. A gemologist can answer the rest without damaging the stone.
Care & handling.
At 3.5 to 4 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with distinct basal cleavage; uneven to splintery fracture, which is worth knowing before you set it or drop it.
Skip the ultrasonic. Lukewarm water, mild soap and a soft cloth handle routine cleaning without risk.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is KAl₃(SO₄)₂(OH)₆. Crystal system: Trigonal. Specific gravity: 2.6 to 2.8. Streak: White. Cleavage and fracture: Distinct basal cleavage; uneven to splintery fracture.
How it reaches the market
Acid-altered volcanic zones; notable: Tolfa (Italy), Spain, Utah (USA, Marysvale), Australia.
What it gets confused with
Limestone/calcite: Calcite fizzes in vinegar; alunite never does. Magnesite: Very similar in hand, magnesite fizzes in warm acid; alunite stays inert. Howlite: Howlite shows gray web veins.
What it is worth
Inexpensive; mainly of field-collector interest.
One more thing
For centuries alunite was roasted to make alum for dyeing cloth, the papacy once ran a lucrative alum monopoly from Tolfa's mines.
An education-first guide.
We do not carry alunite. This page exists because the question comes up and the honest answer is worth writing down, whether or not there is anything here to sell you.
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