The visible diffuse reflectance spectrum in relation to the color and crystal properties of hematite
The visible diffuse reflectance spectrum in relation to the color and crystal properties of hematite
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DOI：
10.1346/ccmn.2003.0510307
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发表时间：
2003-06-01
影响因子：
2.2
通讯作者：
Barrón, V
中科院分区：
文献类型：
--
作者：
Torrent, J;Barrón, V
赤铁矿（α-Fe 2 O3）具有独特的光谱特性，便于在矿物混合物中识别。本文报道了81种天然和人工合成赤铁矿的可见漫反射光谱与颜色和晶体性质的关系。稀释至4 wt.%的粉末状赤铁矿样品的可见DR光谱用BaSO 4白色标准记录并用于计算相应的孟塞尔颜色。利用DR的Kubelka-Munk函数的二阶导数来估计主要吸收带的位置和强度，这些吸收带出现在类似于435、类似于485和类似于545 nm处。孟塞尔色调的范围从9.5P到5.3YR，并且与类似于545 nm的带的位置负相关，因此随着带向更短波长（更高能量）移动，孟塞尔色调变得更黄。Munsell值在4.9 ~ 8.6之间，色度在1.4 ~ 8.3之间，与545 nm附近谱带的强度分别呈负相关和正相关，其位置与Al取代度（x）呈弱负相关。该谱带的位置和强度也与比表面积（SSA）呈弱负相关;然而，两者与通过[110]和[104]方向上的X射线平均相干长度（MCL）之间的比率测量的畴形状无关。类435和类485 nm谱带的性质与x、SSA或MCL 110/MCL 104无关。545 nm带的位置与x的负相关关系不支持将该带归属于2（6A（1））→ 2（T-4（1g）（（4）G））电子对跃迁（EPT），EPT与Fe ~（3+）-Fe ~（3+）共面八面体间的磁耦合有关。类似于485 nm波段可能反映了铁缺陷赤铁矿中的“针铁矿”结构成分，因为它出现在与针铁矿（α-FeOOH）中边共享八面体之间的Fe 3 +-Fe 3+磁耦合相关的假设EPT相同的波长处。
Hematite (alpha-Fe2O3) possesses distinct spectral properties which facilitate its identification in mineral mixtures. This paper reports the relationships between the visible diffuse reflectance (DR) spectrum and the color and crystal properties of a group of 81 natural and synthetic hematites. The visible DR spectra for powdered hematite samples diluted to 4 wt.% with BaSO4 white standard were recorded and used to calculate the corresponding Munsell colors. The second derivative of the Kubelka-Munk function of the DR was used to estimate the position and intensity of the main absorption bands, which occurred at similar to435, similar to485 and similar to545 nm. The Munsell hue ranged from 9.5P to 5.3YR and was negatively correlated with the position of the similar to545 nm band, so it became yellower as the band shifted to shorter wavelengths (higher energies). The Munsell value, which ranged from 4.9 to 8.6, and chroma, which ranged from 1.4 to 8.3, were negatively and positively correlated, respectively, with the intensity of the similar to545 nm band, the position of which exhibited a weak negative correlation with the degree of Al substitution (x). The position and intensity of this band also exhibited a weak negative correlation with the specific surface area (SSA); both, however, were uncorrelated with domain shape as measured by the ratio between the X-ray mean coherence lengths (MCLs) in the [110] and [104] directions. The properties of the similar to435 and similar to485 nm bands were unrelated to x, SSA or MCL110/MCL104. The negative relationship between the position of the similar to545 nm band and x does not support the assignment of this band to the 2(6A(1)) --> 2 (T-4(1g)((4)G)) electron pair transition (EPT), which relates to the to Fe3+-Fe3+ magnetic coupling between face-sharing octahedra. The similar to485 nm band might reflect a 'goethitic' structural component in Fe-defective hematites as it appears at the same wavelength as the hypothetical EPT related to Fe3+-Fe3+ magnetic coupling between edge-sharing octahedra in goethite (alpha-FeOOH).