绿泥石中α=102°的规则一层多型之实际发现

The Real Discovery of the Regular One-layer Chlorite Polytype with α=102°

Bailey等从理论上已推导出绿泥石中共有 12种不同的规则一层多型。其中 2种多型的轴角α =10 2° ,其余 10种则均为α =90° .迄今在自然界已发现的仅有α =90°的 3种规则一层绿泥石多型 (Ⅱb - 2 ,Ⅱb - 4和Ⅰa - 4型 ) .根据透射电镜观察 ,在采自山东泗水圣水峪作为镁普通角闪石蚀变产物的辉绿泥石中 ,发现了由两种不同的规则一层绿泥石多型构成的体衍交生体 ,并确认了其中一种为属于α =10 2°的Ⅰb - 3或Ⅱab - 4的规则一层多型 ;另一种则为α =90°的一种未确定的多型。根据对 [10 0 ]晶带选区电子衍射花样测定的结果 ,该Ⅰb - 3(或Ⅱab - 4 )多型的晶胞参数为c0 =1.4 6 0nm ,b0 =0 .92 6nm及α =10 2° ;此外 ,并可推定其 β≈ 90° ,γ≈ 90°以及a0 ≈ 0 .5 35nm ,空间群为C1或C1.

Bailey et al. has theoretically derived that there are twelve unique regular one?layer polytypes for chlorite. Among them, two are α=102° and the others are α=90°; and only three polytypes (Ⅱb-2,Ⅱb-4 and Ⅰa-4) catalogued in the latter have been discovered in nature so far. By means of transmission electron microscopy, a syntactic intergrowth of two kinds of regular one?layer chlorite polytypes is observed in the diabantite, an alteration product of magnesio?hornblende sampled from Shengshuiyu, Sishui County, Shandong Province, China. One of these two polytypes has been confirmed as type Ⅰb-3 or Ⅱab-4, a regular one-layer polytype with α=102°, and the other is an undetermined one with α=90°. Based on the measured result of zone selected area eletron diffraction pattern, the cell parameters of the polytype Ⅰb-3 (or Ⅱab-4) can be: c 0=1.460 nm, b 0=0.926 nm and α=102°. Besides, it can be inferred that β≈90°, γ≈90° and a 0≈0.535 nm, and C1 or C1 in space group.