硼镁铁矿的新亚种——富锡硼镁铁矿

富锡硼镁铁矿是硼镁铁矿的含锡亚种。它产于湖南常宁县七里坪镁质矽卡岩硼矿床中。矿物中SnO_2变化范围为4.6—12.0%,其分子式为(Mg_1.64Fe~(2+_(0.35))Mn~(2+_(0.01))(Fe~(3+_(0.55))Sn_(0.16)Mg(0.23))BO_5,这是迄今未见详细报导过的。笔者从矿物的光学物理性质、化学成分、X射线晶体学以及晶体化学等方面进行了研究。同时,与它的类似矿物在晶体学方面作了对比讨论。从以上研究中得出结论:Sn~(4+)在结构中占据Fe~(3+)的位置,并以伴随着的Mg~(2+)作电荷补偿。还提出了Sn元素在硼镁铁矿中不仅作为微量元素存在,而且可以作为造种元素存在的新见解。

A New Subspecies of Ludwigite-Tinan Ludwigite

Tinan ludwigite, a new Sn-rich subspecies of ludwigite, occurs in a magnesian skarn borate deposit at Qiliping, Changning County, Hunan province. The SnO_2 content of the mineral varies from 4.6 to 12.0 wt. %, and the chemical formula is (Mg_(1.64)Fe_(0.35)~(2+)Mn_(0.01)_(2.00)(Fe_(0.55)~(3+)Sn_(0.16)Mg_(0.28))_(0.99)BO_5, which has never been previously reported. The authors have studied the mineral in such aspects as its optical and physical properties, chemical composition, X-ray crystallography, and crystallochemistry, with a crystallographic comparison given between this mineral and its analogues.From the above investigation, the authors have come to the conclusion that Fe~(3+) position has been occupied by Sn~(4+) in the crystal structure and the charge is compensated by having Mg~(2+) It is also the authors' opinion that tin not only is a minor component but also serves as a species-forming element ludwigite.