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Sulfate

Alum-(K)

KAl(SO₄)₂·12H₂O
Hardness2.25
Crystal systemCubic
ClassSulfate
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Alum-(K) specimen

Alum-(K) Locality: Alum King Occurrence (Big Star), Henry District, Antelope Range , Sevier County, Utah , USA ( Locality at mindat.org ) Size: 5.4 x 5.0 x 2.7 cm. Lustrous, water-clear to translucent, super sharp, zoned potassium alum crystals from an uncommon Utah locality - the Alum King Mine in Piute County. The piece has neat, stepped triangular form, reflecting the isometric crystal structure. Ex. John Ydren Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0

Alum-(K)

Alum-(K) is a hydrous potassium aluminium sulfate mineral with formula KAl(SO4)2·12(H2O). It is the mineral form of potassium alum and is referred to as potassium alum in older sources. It is a member of the alum group. It occurs as colorless to white, soft isometric crystals and efflorescence coatings. Rare crystals are octahedral in form if occurring as precipitates from neutral water solution, but cubic in form if the solution is alkaline. It occurs as a precipitate around volcanic fumaroles and solfataras.

Intro adapted from Wikipedia (CC BY-SA).

Alum-(K) is an IMA-recognized mineral species in the sulfate class, with the chemical formula KAl(SO₄)₂·12H₂O.

It crystallizes in the cubic crystal system (space group Pa3). It is a member of the Alum structural group.

Key properties: Mohs hardness 2.25; specific gravity 1.757; refractive index 1.453; optically isotropic.

IMA symbol Aum-K, IMA status: approved, named in 1951.

Index entry. This entry combines official IMA/RRUFF species data with published physical-property data and a Wikipedia introduction — a full written entry hasn’t been published yet. Browse more A minerals or help write this entry.