宝石级氟磷锰矿的化学成分及光谱学表征

Chemical Constituents and Spectra Characterization of Gem-Grade Triplite

氟磷锰矿是一种稀有矿物,宝石级氟磷锰矿可呈现高饱和度的红橙色。选取三颗来自巴基斯坦的样品,通过电子探针、拉曼光谱、红外光谱和紫外-可见光吸收光谱进行系统研究,旨在获得其化学成分、光谱学特征,分析致色离子,为其品种鉴定、优化处理等提供重要数据。样品平均化学成分化学式为(Mn_(1.66),Fe_(0.17),Ca_(0.15),Mg_(0.03))_(Σ2.02)[P_(0.99)O_(4.14)]F_(0.82),属含少量铁的氟磷锰矿,与文献记载的巴基斯坦Shigar山谷产出的宝石级氟磷锰矿化学成分相似。拉曼光谱与红外光谱显示氟磷锰矿的主要振动基团为PO_(4)^(2-)基团。拉曼光谱的主峰位于980 cm^(-1),可用于分析羟基与氟的替代关系,450和427 cm^(-1)双峰的强度比可反映Mn^(2+)和Fe^(2+)的替代关系。红外光谱在400~650 cm^(-1)波段和900~1 200 cm^(-1)波段有吸收峰,可以反映羟基与氟和Mn^(2+)与Fe^(2+)的替代关系。因此,拉曼光谱、红外光谱特征可清晰区分氟磷锰矿、羟磷锰矿和氟磷铁矿三个类质同像矿物。紫外-可见光吸收光谱中,以406 nm为中心的强吸收峰是由于Mn^(2+)自旋禁阻跃迁导致;以455 nm为中心的弱吸收峰是由于Fe^(2+)自旋禁阻跃迁导致,Mn^(2+)对此峰也有一定贡献;以533 nm为中心的吸收峰是由Mn^(2+)的^(6)A_(1g)(S)→^(4)T_(1g)(G)跃迁导致。样品呈现红橙色,属自色矿物。氟磷锰矿族矿物普遍存在类质同象,拉曼光谱、红外光谱可准确鉴定氟磷锰矿,电子探针可以为其产地溯源提供重要信息。

Triplite is a rare mineral,and gem-grade triplite can present a highly saturated reddish orange.In this paper,three samples from Pakistan are selected for systematic research through Electron Microprobe,Raman spectra,Infrared spectra and UV-Vis absorption spectra.The purpose is to obtain their chemical composition and spectral characteristic,analyze the chromogenic ions,and provide important data for their species identification and optimization processing.The chemical formula of average chemical composition is(Mn_(1.66),Fe_(0.17),Ca_(0.15),Mg_(0.03))_(Σ2.02)P_(0.99)O_(4.14)(F)_(0.82),which belongs to the Mg-rich and Fe-poor triplite.And it has a similar chemical composition with the gem-grade triplite produced in the Shigar Valley of Pakistan in the literature.Raman spectra and Infrared spectra show that the main vibration group of triplite is PO_(4)^(2-) group.The main peak of Raman spectra is located at 980 cm^(-1),which can be used to analyze the substitution relationship between OH^(-) and F.The intensity contrast of the 450 and 427 cm^(-1) bimodal peaks can reflect the substitution relationship between Mn^(2+) and Fe^(2+).The Infrared spectra has absorption peaks in the 400~650 and 900~1 200 cm^(-1) band,which can reflect the substitution relationship between OH^(-) and F,Mn^(2+) and Fe^(2+).Thus,Raman spectra and Infrared spectra can be used to clearly distinguish the isomorphic minerals:triplite,wolfeite and zwieselite.In the UV-Vis absorption spectra,the strong absorption peak centered at 406 nm is caused by the spin-forbidden transition of Mn^(2+).The weak absorption peak centered at 455 nm is caused by the spin-forbidden transition of Fe^(2+),and Mn^(2+) also has a certain effect on this peak.The absorption peak centered at 533 nm is caused by the transition of Mn^(2+),^(6)A_(1 g)(S)→^(4)T_(1 g)(G).So the samples show a reddish orange color,which is an idiochromatic mineral.There are common isomorphisms in the triplite group minerals.Raman spectra and Infrared spectra can identify triplite accurately,and EMPA can provide important information for the traceability of its origin.