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Crystal of potassium alum, KAl(SO 4) 2 ·12H 2 O. An alum (/ ˈ æ l ə m /) is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula X Al(SO 4) 2 ·12 H 2 O, such that X is a monovalent cation such as potassium or ammonium. [1] By itself, "alum" often refers to potassium alum, with the ...
Alum-(K) is a hydrous potassium aluminium sulfate mineral with formula KAl(SO 4) 2 ·12(H 2 O). 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. [2] It occurs as colorless to white, soft isometric crystals and efflorescence coatings. [3]
Alunite crystals morphologically are rhombohedra with interfacial angles of 90° 50', causing them to resemble cubes. Crystal symmetry is trigonal. Minute glistening crystals have also been found loose in cavities in altered rhyolite. Alunite varies in color from white to yellow gray.
Aluminium sulfate is sometimes called alum or papermaker's alum in certain industries. However, the name " alum " is more commonly and properly used for any double sulfate salt with the generic formula X Al(SO 4 ) 2 ·12H 2 O , where X is a monovalent cation such as potassium or ammonium .
The following table gives the crystalline structure of the most thermodynamically stable form(s) for elements that are solid at standard temperature and pressure.Each element is shaded by a color representing its respective Bravais lattice, except that all orthorhombic lattices are grouped together.
Ammonium aluminium sulfate, also known as ammonium alum or just alum (though there are many different substances also called "alum"), is a white crystalline double sulfate usually encountered as the dodecahydrate, formula (NH 4)Al(SO 4) 2 ·12H 2 O. It is used in small amounts in a variety of niche applications.
The ancients are known to have used alum as a dyeing mordant and for city defense. [75] After the Crusades, alum, an indispensable good in the European fabric industry, [76] was a subject of international commerce; [77] it was imported to Europe from the eastern Mediterranean until the mid-15th century. [78] The nature of alum remained unknown.
Forsterite. In chemistry, isomorphism has meanings both at the level of crystallography and at a molecular level. In crystallography, crystals are isomorphous if they have identical symmetry and if the atomic positions can be described with a set of parameters (unit cell dimensions and fractional coordinates) whose numerical values differ only slightly.