Time resolved in situ X-ray diffraction was used to study the formation of vanadyl hydrogen phosphate hemihydrate (VOHPO4.0.5H(2)O) in organic media. This technique has identified a new phase at early synthesis times (less than 300 s) at a d-spacing of 7.5 and 3.1 Angstrom. The feature at 7.5 Angstrom shifted to 6.7 Angstrom during the first 20 min of synthesis and this phase collapsed as VOHPO4.0.5H(2)O formed. Thin symmetrical platelets of 10 mum x 10 mum dimensions were observed when samples were recovered after short synthesis times. Energy dispersive X-ray analysis indicated that these platelets contained vanadium and phosphorus. The platelets appeared to delaminate possibly associated with the strain generated when the d-spacing shifted from 7.5 to 6.7 Angstrom, from which growth of the VOHPO4.0.5H(2)O into the familiar rosette morphology occurs. (C) 2004 Elsevier B.V. All rights reserved.