X-ray Study of the Structure of Sepiolite

Anton Preisinger
Mineralog. Institut, Universität Wien, Austria

Abstract: Sepiolite is a valid mineral with the following chemical formula: 8MgO⋅12Si O 2 ⋅n H 2 O.

Its unit cell characteristics are: a=13.4Å;  b=26.8χ;  c=5.28Å;  Z=2;  D 6 2 h−P 2 1 n 2 c 2 n . They were determined on the sepiolite from Ampandrandava (Madagascar). Its structure was determined by means of the “trial and error” method and the observed and calculated intensities rendered a good agreement.

The formula of the structure is: 1 ∞ [ H 2 O ] n ⋅ 1 ∞ { ( Mg,Fe 3+ , Fe 2+ ,Al ) 8 ( H 2 O ) 4 ( O,OH ) 4 [ ( Si,Al ) 10 O 30 ] }⋅n⩽8.

The mineral contains zeolitic, crystal- and constitution-water. A good agreement was achieved between the chemical, thermal, and morphological qualities and the x-ray data. The mineral remains stable up to about 350°C and begins to change into an “anhydride” above this temperature.

The formula of the structure of sepiolite-“anhydride” is: 1 ∞ { ( Mg,Fe 3+ , Fe 2+ ,Al ) 8 ( O,OH ) 4 [ ( Si,Al ) 10 O 30 ] }.

Its unit cell characteristics are: a=10.9Å;  b=23.3Å;  c=5.28Å;  a≈90°;  Z=2;  C 5 2 h−P 2 1 n 11.

The minerals xylotile, mountain wood and gunnbjarnite are isotypical with sepiolite.

Clays and Clay Minerals; 1959 v. 6; no. 1; p. 61-67; DOI: 10.1346/CCMN.1957.0060106
© 1959, The Clay Minerals Society
Clay Minerals Society (www.clays.org)