TY - JOUR

T1 - Natural bentorite—Cr3+ derivate of ettringite

T2 - determination of crystal structure

AU - Seryotkin, Yurii V.

AU - Sokol, Ella V.

AU - Kokh, Svetlana N.

AU - Sharygin, Victor V.

N1 - Publisher Copyright: © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.

PY - 2019/6/1

Y1 - 2019/6/1

N2 - Bentorite, a Cr3+-substituted analogue of ettringite (Ca6Cr2(SO4)3(OH)12·26H2O), has been found as veinlet filling at its holotype locality in the Hatrurim Basin (Negev Desert). Quite abundant massive bentorite with Cr/(Cr + Al) ratios up to 0.95–0.99 coexists with sporadic portlandite, gypsum, afwillite, truscottite, fluorapatite, tobermorite, calcite, and vaterite. It occurs as almost monomineralic clots composed of fibrous grains. The crystal structure of bentorite has been determined and refined for the first time by XRD powder diffraction coupled with high-accuracy synchrotron low-temperature measurements at 100, 250 K and 295 K. Bentorite is isostructural with ettringite, space group P31c. The analysed bentorite sample has a trigonal unit cell with the parameters a = 11.16150(5), c = 21.63017(19) Å, V = 2333.650(19) Å3 at 100 K; a = 11.17790(5), c = 21.7375(2) Å, and V = 2352.12(2) Å3 at 250 K, and a = 11.2110(2), c = 21.7654(7) Å, and V = 2369.10(7) Å3 at 295 K. The bentorite structure includes only (SO4)2−-groups, three anions per formula unit, as in ettringite. Unlike ettringite, bentorite has Cr3+ instead of Al3+ cations, this being the only difference in chemistry. The obtained structure confirms the existence of a continuous series of ettringite Ca6Al2M[SO4]3R(OH)12·26H2O–bentorite Ca6Cr2M[SO4]3R(OH)12·26H2O solid solutions over the whole range 0 ≤ Cr3+/(Al + Cr3+) ≤ 1.

AB - Bentorite, a Cr3+-substituted analogue of ettringite (Ca6Cr2(SO4)3(OH)12·26H2O), has been found as veinlet filling at its holotype locality in the Hatrurim Basin (Negev Desert). Quite abundant massive bentorite with Cr/(Cr + Al) ratios up to 0.95–0.99 coexists with sporadic portlandite, gypsum, afwillite, truscottite, fluorapatite, tobermorite, calcite, and vaterite. It occurs as almost monomineralic clots composed of fibrous grains. The crystal structure of bentorite has been determined and refined for the first time by XRD powder diffraction coupled with high-accuracy synchrotron low-temperature measurements at 100, 250 K and 295 K. Bentorite is isostructural with ettringite, space group P31c. The analysed bentorite sample has a trigonal unit cell with the parameters a = 11.16150(5), c = 21.63017(19) Å, V = 2333.650(19) Å3 at 100 K; a = 11.17790(5), c = 21.7375(2) Å, and V = 2352.12(2) Å3 at 250 K, and a = 11.2110(2), c = 21.7654(7) Å, and V = 2369.10(7) Å3 at 295 K. The bentorite structure includes only (SO4)2−-groups, three anions per formula unit, as in ettringite. Unlike ettringite, bentorite has Cr3+ instead of Al3+ cations, this being the only difference in chemistry. The obtained structure confirms the existence of a continuous series of ettringite Ca6Al2M[SO4]3R(OH)12·26H2O–bentorite Ca6Cr2M[SO4]3R(OH)12·26H2O solid solutions over the whole range 0 ≤ Cr3+/(Al + Cr3+) ≤ 1.

KW - Bentorite

KW - Bentorite–ettringite solid solutions

KW - Chromium

KW - Crystal structure

KW - MINERALS

KW - RAMAN-SPECTROSCOPY

KW - ORGANIC-MATTER

KW - Bentorite-ettringite solid solutions

KW - MOTTLED ZONE

KW - CR

KW - ORIGIN

KW - SOLID-SOLUTION

KW - AREA

KW - DIFFRACTION

KW - DEAD-SEA

UR - http://www.scopus.com/inward/record.url?scp=85060822301&partnerID=8YFLogxK

U2 - 10.1007/s00269-019-01022-4

DO - 10.1007/s00269-019-01022-4

M3 - Article

AN - SCOPUS:85060822301

VL - 46

SP - 553

EP - 570

JO - Physics and Chemistry of Minerals

JF - Physics and Chemistry of Minerals

SN - 0342-1791

IS - 6

ER -