Crystals

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General Information

Potassium Alum

Potassium alum is one of the possible combinations of alum. There is also chrome alum and ammonium alum.[1]

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Production Methods

Potassium alum crystals are very clear when they are grown slowely. This easiest way to do this is by evaporating a saturated solution. Cooling down a supersaturated solution has to be done slowely (using proper isolation) to prevent the crystals from become slightly opaque. Chrome alum can be combined with potassium alum to make light purple crystals. It's also possible to make a crystal that gets gradually lighter from the center outward by using a solution with an increasing amount of potassium alum dissolved in it.[1]

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Chemical & Physical Information

Trivial namePotassium alum
Chemical namePotassium aluminium sulfate, dodecahydrate
Other namesAluin (NL,BE)
Type of chemicalIonic compound (salt)
Chemical formulaKAl(SO4)2, 12H2O
CAS number7784-24-9
Crystal systemCubic
Bravais laticeCubic
Coordination geometryOctahedral
ColourWhite
LusterVitreous
StreakWhite
OpacityTranslucent to transparent
Safety summarySafe
Safety dataMSDS
Production methodSolution vaporization, supersaturated solution cooling.
StorageDry
Extra-

For more information, also look at the potassium alum chemicals.

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Photos

Potassium Alum

(3 cm)

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Sources

[1] Wikipedia

[2] Specimen from my personal collection, photo taken by me.