Spiral Crystal Growth of Potassium Dichromate in Gelatin

Abstract

Huge spiral crystals of potassium dichromate (K₂Cr₂O₇)have been found to grow three-dimensionally in a gelatin medium when gelatincontaining K₂Cr₂O₇ was dried slowly in a test tube at a lowtemperature.These spirals were all right-handed, and their widths, axial pitches andlengths were 2--3, mm, 5--6, mm and 20--25, mm, respectively. When the gelatinconcentration in the medium was decreased, ordinary platelike crystals were observed to grow, instead of the spiral crystals. To the best of our knowledge, inorganiccompounds such as K₂Cr₂O₇ have so far not been reported toform such huge spiral crystals.It is conjectured that collagen molecules, which compose the gelatinmedium and have right-handed triple helix structure lead to the growth of spiralcrystals.