Crystals

Top

General Information

Chrome Alum

Chrome alum is one of the possible combinations of alum. There is also potassium alum and ammonium alum. Chrome alum was formerly used in the leather tanning industry. It normally forms a dodecahydrate, but it can also form monohydrates (H2O), dihydrates (2H2O) and hexahydrates (6H2O).[1]

Top

Production Methods

Chrome alum crystals are very dark purple when they are made solely from chrome alum. 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]

Top

Chemical & Physical Information

Trivial nameChrome alum
Chemical nameChromium(III) potassium sulfate, dodecahydrate
Other namesChroom aluin (NL,BE)
Type of chemicalIonic compound (salt)
Chemical formulaKCr(SO4)2, 12H2O
CAS number10141-00-1 (anhydrous)
7788-99-0 (dodecahydrate)
Crystal systemCubic
Bravais latticeCubic
Coordination geometryOctahedral
Hardness (Mohs)?
Young's modulus?
ColourPurple
LusterVitreous
StreakPurple
OpacityTranslucent to transparent
Safety summarySafe
Safety dataMSDS
Production methodSolution vaporization, supersaturated solution cooling.
StorageDry and below 50 °C.
Extra-

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

Top

Photos

Chrome Alum

(1 cm)

Top

Sources

[1] Wikipedia

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