Open AccessThe structure of cyanite, Al 2 SiO 5
Publication year - 1928
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1928.0088
Subject(s) - andalusite , triclinic crystal system , orthorhombic crystal system , crystallography , face (sociological concept) , sillimanite , space (punctuation) , unit (ring theory) , plane (geometry) , crystal (programming language) , class (philosophy) , crystal structure , materials science , chemistry , geometry , mathematics , computer science , geology , metallurgy , artificial intelligence , petrology , social science , quartz , sociology , metamorphism , operating system , programming language , mathematics education , biotite
The three naturally occurring forms of Al2 SiO5 have been examined by Mark and Rosbaud, who have determined the space-groups of the orthorhombic forms (andalusite and sillimanite) and the unit cell of cyanite, which belongs to the pinacoidal class of the triclinic system. The present paper contains an account of the determination of the arrangement of the atoms in cyanite. The analysis of this structure is interesting from two points of view. In the first place, it is of special interest to the mineralogist because it is probably the most striking example of a crystal which exhibits different degrees of hardness in different directions on the same face. The measured values of the hardness on the (100) face of cyanite are 4-5 in a direction parallel to thec axis and 6-7 in a direction parallel to the edge common to the (100) and (001) faces. Any suggested structure must, of course, explain this unusually large variation.