LAUE DATA REFINEMENT OF THE CRYSTAL STRUCTURE OF STANFIELDITE, DATA COLLECTED AT CHESS USING UNDULATOR RADIATION WITH IMAGE PLATES IN A CYLINDRICAL FILM CASSETTE Joseph J. Pluth and Ian M. Steele, Department of Geophysical Sciences and CARS, Alan LeGrande and Zhong Ren, Department of Biochemistry and Molecular Biology and CARS, The University of Chicago, Chicago, IL 60637

X-ray Laue diffraction data were obtained for Stanfieldite using an exposure time of 0.05 seconds per frame for 9 frames. The data were processed using LaueView (Ren, Moffat, J. Appl. Cryst. (1995) 28,461).

Sample Source: stony-iron meteorite

Ca4.05Mg4.55Fe0.32Mn0.05P6O24

Space Group C2/c

Unit Cell: 22.813(3) 9.993(1) 17.090(1) 99.96(1)

Crystal Size 0.06 x 0.1 x 0.2 mm3

Monochromatic Laue

X-ray wavelength 0.71069 0.7 - 3.0

exposure time 567360 sec (~6.6 days) 0.45 sec

Unique diffractions 6928 8475

R 0.047 0.1841

Rw 0.041 0.1650

Parameters varied 359 359

Although the R values for the Laue refinement remained high, the results are in good agreement with the monochromatic data set. See below for a partial listing of atom parameters (1st line monochromatic, 2nd Laue):

Atom x y z Ueq

Ca5 0.06597(2) 0.10401(6) 0.58830(3) 0.0155(2)

Ca5 0.06608(8) 0.1041(2) 0.58843(14) 0.0187(6)

Mg5 0.42063(3) 0.09020(7) 0.55203(4) 0.0089(2)

Mg5 0.42062(10) 0.0906(2) 0.5522(2) 0.0107(8)

P1 0.18317(2) 0.11846(5) 0.10024(3) 0.00689(13)

P1 0.18335(7) 0.11856(15) 0.10017(13) 0.0099(5)

O1 0.24338(6) 0.0845(2) 0.15538(9) 0.0095(4)

O1 0.2435(2) 0.0841(5) 0.1550(4) 0.0138(15)