台湾红壤及森林土壤中之氧化铁

IRON OXIDES DISTRIBUTED IN RED AND FOREST SOILS OF TAIWAN

本文综合汇整近年来在台湾，应用高梯度磁场分离技术，配合一般化学分析，Ｘ－射线衍射法，磁测分析，电子显微镜观察与电子衍射鉴定，以及铁－５７穆斯堡尔谱学分析等方法，研究红壤与森林土壤中，氧化铁的分布及其结构性质之成果回顾；关于氧化铁之分布情形，其研究结果显示：台湾红壤中普遍存在有赤铁矿与针铁矿等氧化铁矿物，而在化育自大屯山更新世纪安山岩母质与澎湖列岛更新世纪玄武岩母质的红壤中，以及兰屿绿岛海边之银白色海砂，由于亦存在有磁铁矿与磁赤铁矿等强磁性矿物，致使其具有强磁感率。在寿卡一带之红壤以及标高约２０００ｍ高山的森林土壤中，则发现含有纤铁矿，利用Ｘ－射线衍射鉴定以及穆斯堡尔谱学分析，证实寿卡红壤经高梯度磁分离后之磁性粘粒部分，含有针铁矿、纤铁矿，晶性不良之赤铁矿，以及含铁绿泥石，其中含铁绿泥石构造中之两价铁，乃位于类似滑石之顺式配位座落中；而从电子显微镜观察高山灰化土中，与纤铁矿共存之针铁矿，发现其为表面平滑，透光度规则之条状晶体，以电子衍射鉴定证实此构形乃由钉铁矿（１００）面上俯瞰之结果。

his paper summarizes the distribution of iron oxides in red and forest soils ofTaiwan,using the high gradient magnetic separation(HGMS)technique. Soil ironoxides were measured by the methods including wet chemistry,X-ray diffraction(XRD),magnetic measurement,transmission electron microscope(TEM)and electrondiffraction,Fe-57 Mossbauer analysis,etc. Acidic red soils developed from andesi-tic rocks of Ta-Tun,and Lu-Tau, Lau-Hsu and Peng-Hu calcareous red soils develo-ped from basaltic rocks showed high magnetic susceptibility and contained ferrima-gnetic minerals of magnetite or maghemite. Goethite and/or hematite could be identi-fied in the most red soils.The clays accumulated in B horizons of the Shou-Ka soils and podzols occurringon high mountains were found to contain lepidocrocite. Magnetic clay fractions ofSbou-Ka soils cliaracterized by XRD and Fe-57 Mossbauer analysis showed that Shou-Ka soils contained goethite,lepidocrocite, poor crystalline hematite and iron-richchlorite.Structural Fe￣(2+) in iron-rich chlorite was located at talc-like cis-OH(M2)sites.The observations of TEM and electron diffraction of forest soils showed thatgoethite was lath-shape and indexed as(100)plane.