TY - JOUR

T1 - Structure refinement and thermal stability studies of the uranyl carbonate mineral andersonite, Na 2 Ca[(Uo 2 )(CO 3 ) 3 ]·(5+x)H 2 O

AU - Gurzhiy, Vladislav V.

AU - Krzhizhanovskaya, Maria G.

AU - Izatulina, Alina R.

AU - Sigmon, Ginger E.

AU - Krivovichev, Sergey V.

AU - Burns, Peter C.

PY - 2018/12/11

Y1 - 2018/12/11

N2 - A sample of uranyl carbonate mineral andersonite, Na 2 Ca[(UO 2 )(CO 3 ) 3 ]·5−6H 2 O, originating from the Cane Springs Canyon, San Juan Co., UT, USA was studied using single-crystal and powder X-ray diffraction at various temperatures. Andersonite is trigonal, R−3m, a = 17.8448(4), c = 23.6688(6) Å, V = 6527.3(3) Å 3 , Z = 18, R 1 = 0.018. Low-temperature SCXRD determined the positions of H atoms and disordered H 2 O molecules, arranged within the zeolite-like channels. The results of high-temperature PXRD experiments revealed that the structure of andersonite is stable up to 100 ◦ C; afterwards, it loses crystallinity due to release of H 2 O molecules. Taking into account the well-defined presence of H 2 O molecules forming channels’ walls that to the total of five molecules p.f.u., we suggest that the formula of andersonite is Na 2 Ca[(UO 2 )(CO 3 ) 3 ]·(5+x)H 2 O, where x ≤ 1. The thermal behavior of andersonite is essentially anisotropic with the lowest values of the main thermal expansion coefficients in the direction perpendicular to the channels (plane (001)), while the maximal expansion is observed along the c axis—in the direction of channels. The thermal expansion around 80 ◦ C within the (001) plane becomes negative due to the total release of “zeolitic” H 2 O molecules. The information-based structural complexity parameters of andersonite were calculated after the removal of all the disordered atoms, leaving only the predominantly occupied sites, and show that the crystal structure of the mineral should be described as complex, possessing 4.535 bits/atom and 961.477 bits/cell, which is comparative to the values for another very common natural uranyl carbonate, liebigite.

AB - A sample of uranyl carbonate mineral andersonite, Na 2 Ca[(UO 2 )(CO 3 ) 3 ]·5−6H 2 O, originating from the Cane Springs Canyon, San Juan Co., UT, USA was studied using single-crystal and powder X-ray diffraction at various temperatures. Andersonite is trigonal, R−3m, a = 17.8448(4), c = 23.6688(6) Å, V = 6527.3(3) Å 3 , Z = 18, R 1 = 0.018. Low-temperature SCXRD determined the positions of H atoms and disordered H 2 O molecules, arranged within the zeolite-like channels. The results of high-temperature PXRD experiments revealed that the structure of andersonite is stable up to 100 ◦ C; afterwards, it loses crystallinity due to release of H 2 O molecules. Taking into account the well-defined presence of H 2 O molecules forming channels’ walls that to the total of five molecules p.f.u., we suggest that the formula of andersonite is Na 2 Ca[(UO 2 )(CO 3 ) 3 ]·(5+x)H 2 O, where x ≤ 1. The thermal behavior of andersonite is essentially anisotropic with the lowest values of the main thermal expansion coefficients in the direction perpendicular to the channels (plane (001)), while the maximal expansion is observed along the c axis—in the direction of channels. The thermal expansion around 80 ◦ C within the (001) plane becomes negative due to the total release of “zeolitic” H 2 O molecules. The information-based structural complexity parameters of andersonite were calculated after the removal of all the disordered atoms, leaving only the predominantly occupied sites, and show that the crystal structure of the mineral should be described as complex, possessing 4.535 bits/atom and 961.477 bits/cell, which is comparative to the values for another very common natural uranyl carbonate, liebigite.

KW - Andersonite

KW - Carbonate

KW - Crystal structure

KW - Minerals

KW - Structural complexity

KW - Uranium

KW - X-ray diffraction

UR - http://www.scopus.com/inward/record.url?scp=85062826167&partnerID=8YFLogxK

U2 - 10.3390/min8120586

DO - 10.3390/min8120586

M3 - Article

AN - SCOPUS:85062826167

VL - 8

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 12

M1 - 586

ER -