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 to the Ertsberg East Cu, Au, and Ag mine in central Irian Jaya, Indonesia. The name is after Jean Jacques Dozy, the Dutch geologist who discovered and named the Ertsberg ore province in 1936. Unit-cell parameters are a = 5.323(3), b = 9.214(9), c = 21.45(2) A, β= 94.43(6)°, and V = 1049(2) Å .It has space group Cm. There is a 21-Å periodicity in the 00l and in most other reflections where k = 3n. The reflections where k ≠3n are continuously streaked. Excellent regularity of alternation of the component serpentine and chlorite units is indicated by the coefficient of variation CV = 0.26 for the 001 reflections. A simplified ideal bulk composition is (Mg Al )(Si Al )O - (OH) with Z = 2, halfway between the compositions of the closely associated discrete chlorite (clinochlore) and the discrete serpentine (amesite). We believe the components in this occurrence of dozyite are clinochlore and amesite and that the interstratification was formed during the conversion of early clinochlore to amesite by Al metasomatism. The structure of dozyite contains a la chlorite unit followed by a serpentine 1:1 layer that is in the same position that the lower tetrahedral sheet of a repeating chlorite unit would occupy in the one-layer monoclinic Iaa-2 chlorite polytype, but rotated 180° so that the octahedral cations alternate I,I,II per 21 Å. The next chlorite unit follows with zero shift of its lower sixfold rings relative to those of the serpentine 1:1 layer. A second occurrence of dozyite has been recognized in a Cr-rich serpentinite from the Wood Chrome mine in Lancaster County, Pennsylvania. It represents a different polytype, with β= 90°, and a different composition relative to the Ertsberg material.