DOZYITE, A 1 1 REGULAR INTERSTRATIFICATION OF SERPENTINE AND CHLORITE/

Dozyite is a new mineral species involving regular interstratification of trioctahedral serpentine and trioctahedral chlorite units in a 1:1 ratio. It occurs as colorless crystals in an altered skarn adjacent t o the Ertsberg East Cu, Au, and Ag mine in central Irian Jaya, Indones ia. The name is after Jean Jacques Dozy, the Dutch geologist who disco vered and named the Ertsberg ore province in 1936. Unit-cell parameter s are a = 5.323(3), b = 9.214(9), c = 21.45(2) Angstrom, beta = 94.43( 6)degrees, and V= 1049(2) Angstrom(3). If has space group Cm. There is a 21-Angstrom periodicity in the 00l and in most other reflections wh ere k = 3n. The reflections where k not equal 3n are continuously stre aked. Excellent regularity of alternation of the component serpentine and chlorite units is indicated by the coefficient of variation CV = 0 .26 for the 00l reflections. A simplified ideal bulk composition is (M g7Al2)(Si4Al2)O-15-(OH)(12) with Z = 2, halfway between the compositio ns of the closely associated discrete chlorite (clinochlore) and the d iscrete serpentine (amesite). We believe the components in this occurr ence of dozyite are clinochlore and amesite and that the interstratifi cation was formed during the conversion of early clinochlore to amesit e by Al metasomatism. The structure of dozyite contains a Ia chlorite unit followed by a serpentine 1:1 layer that is in the same position t hat the lower tetrahedral sheet of a repeating chlorite unit would occ upy in the one-layer monoclinic Iaa-2 chlorite polytype, but rotated 1 80 degrees so that the octahedral cations alternate I,I,II per 21 Angs trom. The next chlorite unit follows with zero shift of its lower sixf old rings relative to those of the serpentine 1:1 layer. A second occu rrence of dozyite has been recognized in a Cr-rich serpentinite from t he Wood Chrome mine in Lancaster County, Pennsylvania. It represents a different polytype, with beta = 90 degrees, and a different compositi on relative to the Ertsberg material.