Crystals
TopGeneral Information
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]
TopProduction 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]
TopChemical & Physical Information
| Trivial name | Chrome alum |
| Chemical name | Chromium(III) potassium sulfate, dodecahydrate |
| Other names | Chroom aluin (NL,BE) |
| Type of chemical | Ionic compound (salt) |
| Chemical formula | KCr(SO4)2, 12H2O |
| CAS number | 10141-00-1 (anhydrous) 7788-99-0 (dodecahydrate) |
| Crystal system | Cubic |
| Bravais lattice | Cubic |
| Coordination geometry | Octahedral |
| Hardness (Mohs) | ? |
| Young's modulus | ? |
| Colour | Purple |
| Luster | Vitreous |
| Streak | Purple |
| Opacity | Translucent to transparent |
| Safety summary | Safe |
| Safety data | MSDS |
| Production method | Solution vaporization, supersaturated solution cooling. |
| Storage | Dry and below 50 °C. |
| Extra | - |
For more information, also look at the chrome alum chemicals.
TopPhotos
(1 cm)
Sources
[1] Wikipedia
[2] Specimen from my personal collection, photo taken by me.
