Internal texture and abnormal optical property of apophyllite
Akizuki, Mizuhiko; Konno, Hiroshi
Neues Jahrbuch für Mineralogie - Abhandlungen Band 151 Heft 1 (1985), p. 99 - 115
32 references
published: Feb 15, 1985
ArtNo. ESP154015101005, Price: 29.00 €
Abstract
The chemical composition of apophyllite may be defined as (K, Na)Ca4Si8-xAlxO20(OH, F)i-x • 8H2O. Although potassium apophyllite crystals show no deviations from the tetragonal system in X-ray analysis, most of the crystals are optically biaxial. The internal textures show that the biaxial structure was produced by atomic order-disorder growth mechanism suggested by Akizuki (1981a). Therefore, some possible explanations for the abnormal optical property were explored from the standpoint of this mechanism. Apophyllite crystals contain more or less aluminum, and Al/Si ordering may occur on the surface during growth, or O-H bond may orient on the surface during growth, resulting in biaxial crystal. The (110) face consists of vicinal faces, on which growth steps move in two opposite directions ([110] and [110]) to each other, and two corresponding ordered structures are in the twin relation.
Keywords
Apophyllite • chemical composition • optical property • internal texture • atomic ordering