Cesium Chromium(III) Disulfate Dodecahydrate

Cesium Chromium Alum · Cesium Alum · Chromium Alum · Alum

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Description

Cesium Chromium(III) Disulfate Dodecahydrate is a striking member of the Alum family, known for its saturated coloration and well-defined geometric crystals. In its pure form, this compound typically crystallizes as a black octahedron with triangular sliced edges. The presence of Chromium(III) gives the crystals their characteristic deep violet hue, which intensifies as the crystal grows. Under bright light, the color shifts between warm magenta and cooler bluish tones depending on the viewing angle.

When mixed with other Cesium Alums—such as Cesium Iron(III) Disulfate Dodecahydrate—the color can vary notably. Mixed crystals often display gentle gradients rather than uniform pigmentation: pale lavender toward the edges and deep violet toward the core.

Cesium Chromium(III) Disulfate Dodecahydrate tends to grow slowly but cleanly in solution, forming unique octahedra with triangular sliced edges. When grown with care, without Non-Alum impurities or significant temperature fluctuations, they can achieve gemstone-like brilliance that makes them particularly appealing to collectors and crystal growers.

Requirements



Synthesis and Crystal Growth Procedure


Begin by preparing saturated aqueous solutions of 150 grams Potassium Chromium(III) Sulfate Dodecahydrate. Important: dissolve the compound in water no warmer than room temperature. Heating produces a hypersoluble modification that prevents proper crystallization. Prepare a separate saturated solution of 50 grams of any readily soluble Cesium Salt, such as CsCl, CsBr, CsI, CsNO3. When the two solutions are combined, a cation-exchange reaction occurs according to the following general equation: KCr(SO4)2*12H2O + CsX = CsCr(SO4)2*12H2O(s) + KX, where X is the corresponding anion. Because Cesium Chromium(III) Disulfate Dodecahydrate is significantly less soluble than Potassium Chromium(III) Sulfate Dodecahydrate, a dark purple precipitate will immediately form.


For reference, the specific reactions are as follows:


KCr(SO4)2*12H2O + CsCl = CsCr(SO4)2*12H2O(s) + KCl

KCr(SO4)2*12H2O + CsBr = CsCr(SO4)2*12H2O(s) + KBr

KCr(SO4)2*12H2O + CsI = CsCr(SO4)2*12H2O(s) + KI

KCr(SO4)2*12H2O + CsNO3 = CsCr(SO4)2*12H2O(s) + KNO3

Remove the supernatant solution and wash the precipitate several times with ice-cold water. At this stage, you have obtained Cesium Chromium(III) Disulfate Dodecahydrate. Dissolve the precipitate in the minimum possible amount of room-temperature water; this step may require several days. Avoid adding excess water. If available, introduce a few drops of Sulfuric Acid to suppress hydrolysis.


If increased transparency of the final crystals is desired, prepare a saturated Cesium Iron(III) Disulfate Dodecahydrate solution and mix approximately 300 ml of it with 50 ml of the Cesium Chromium(III) Disulfate Dodecahydrate solution. Using a smaller proportion of Cesium Iron(III) Disulfate Dodecahydrate will result in crystals that remain very dark (Cesium Aluminium Sulfate Dodecahydrate is almost insoluble in water and therefore unsuitable).


Insert a fishing line into the solution and leave the system undisturbed until seed crystals begin to form. Once the crystals reach a suitable size, carefully remove excess crystals so that only one or two remain attached to each line. Transfer the saturated solution into a clean vessel, collect any residual precipitate (which may be redissolved to produce additional solution), and place the fishing line with the selected crystals into the fresh solution to continue growth. Inspect the crystals periodically and remove new growths that form on the line to prevent undesirable fusion with the main crystal.


After approximately one to two months, large, stable crystals will form. Detach the crystal from the fishing line with care. Cesium Chromium(III) Disulfate Dodecahydrate remain stable under normal atmospheric conditions; therefore, no protective coating (such as nail polish) is required.