Abstract: The (Si,Al)-ordered Be end-member of the cordierite group, sekaninaite, from its type locality at Dolni Bory, Czech Republic, was analyzed, and found to contain 0.04 - 0.24 Li and 0.11 - 0.26 Na apfu; (Fe + Mn)/(Mg + Fe + Mn) (at.) ranges from 0.74 to 0.97. Lithium is incorporated by the substitution (NaLi)-Na-ch-Li-VI(Mg,Fe)(-1). This sekaninaite is the first member of the cordierite group reported to have substantial Li but negligible Be. All samples of Na,Be-, Na,Li,Be- and Na,Li-bearing cordierite-sekaninaite examined to date show a minor deficit in the tetrahedral site (0.237 in the literature, 0.036 in our data) and a slight excess of channel cations (Na,K,Ca) over the proportion of (Be,Li) (at.). The Li-bearing sekaninaite comes from rather simple granitic pegmatites, in which the only Li-bearing minerals are rare triphylite and cookeite. Thus cordierite-group minerals are crystal-chemical sinks for Li. This finding stresses the need to analyze for trace light elements, even in minerals from poorly fractionated and rare-element-depleted environments, provided the crystal chemistry is favorable.
Lithium in sekaninaite from the type locality, Dolni Bory, Czech Republic
1997
Abstract
Abstract: The (Si,Al)-ordered Be end-member of the cordierite group, sekaninaite, from its type locality at Dolni Bory, Czech Republic, was analyzed, and found to contain 0.04 - 0.24 Li and 0.11 - 0.26 Na apfu; (Fe + Mn)/(Mg + Fe + Mn) (at.) ranges from 0.74 to 0.97. Lithium is incorporated by the substitution (NaLi)-Na-ch-Li-VI(Mg,Fe)(-1). This sekaninaite is the first member of the cordierite group reported to have substantial Li but negligible Be. All samples of Na,Be-, Na,Li,Be- and Na,Li-bearing cordierite-sekaninaite examined to date show a minor deficit in the tetrahedral site (0.237 in the literature, 0.036 in our data) and a slight excess of channel cations (Na,K,Ca) over the proportion of (Be,Li) (at.). The Li-bearing sekaninaite comes from rather simple granitic pegmatites, in which the only Li-bearing minerals are rare triphylite and cookeite. Thus cordierite-group minerals are crystal-chemical sinks for Li. This finding stresses the need to analyze for trace light elements, even in minerals from poorly fractionated and rare-element-depleted environments, provided the crystal chemistry is favorable.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
