浙江省青田县的青田石为我国四大图章石之一。 青田石均为原生矿, 属于硐采图章石。 开采出的青田石具有丰富的颜色, 但是其中红色品种的青田石较少, 一般为特征的暗红棕色。 对产自青田县山口矿区的4种红色青田石: 红花冻、 红花、 石榴红、 桔红石进行了谱学研究, 主要采用了偏光显微镜、 X射线粉末衍射(XRD)、 以及拉曼光谱(LRM)对组成它们的主要和次要矿物成分和颜色成因进行了初步探究。 在偏光显微镜下, 对四种红色青田石薄片样品中颜色的分布形态进行了详细观察。 其中, 红花冻和桔红石的红色部分呈颗粒状、 团块状浸染分布于基体中, 而石榴红和红花的红色部分呈点状、 脉状侵染分布于基体中。 在XRD测试中, 对它们的主要矿物成分和次要矿物成分进行了研究, 并对其进行了青田石种类归属。 红花冻、 红花和石榴红的主要矿物成分为叶腊石, 三者属于叶腊石型青田石。 叶腊石存在1Tc和2M两种多型。 根据XRD衍射谱中19°~22°(2θ)和28~31°(2θ)处衍射峰形态和具体峰位, 可知红花冻主要为2M型叶腊石组成, 含有1Tc型叶腊石; 红花和石榴红主要为2M型叶腊石组成。 其中红花冻的次要矿物成分为地开石, 红花的次要矿物成分为石英, 石榴红的次要矿物成分为云母; 桔红石的主要矿物成分为地开石, 属于地开石型青田石。 地开石存在有序→无序的结构特征, 根据地开石XRD的(020), (110)和(112)衍射峰强度特征, 可知石榴红中地开石的有序度较高。 桔红石中次要矿物成分为石英。 拉曼光谱对红色青田石的次要和微量矿物成分进行了研究, 并主要对红色部分的矿物成分进行了探测, 以确定红色青田石的颜色成因。 测试结果显示, 四种红色青田石均含有赤铁矿。 此外, 红花冻中还存在硬水铝石和金红石; 红花中还含有大量石英以及少量硬水铝石和金红石; 石榴红中还含有硬水铝石和金红石; 桔红石中还含有石英。 红花冻、 红花和桔红石为赤铁矿微晶致色, 而石榴红的为金红石微晶致色。 因此, 所研究的四种红色青田石均属于杂质矿物致色。

The Qingtian stone is one the Four famous Seal Stones in China, which is from Qingtian County, Zhejiang Province. All of the Qingtian Stones are primary ore, belonging to mined Seal Stone. The digged Qingtian Stone has various colors. The red Qingtian stone is not an abundant species among Qingtian stones, which shows unique dark reddish brown. Four kinds of red Qingtian Stones have been studied in this paper, which are Jelly Flower-red Stone, Flower-red Stone, Pomegranate-red stone and Orange-red stone. Their mineral composition and color causingare studied by means of optical microscopy, X-ray powder diffraction (XRD), and Raman spectrum (LRM). Under optical microscopy, the red color distribution had been carefully observed in the slices of four kinds of red Qingtian Stones. The red parts of Jelly Flower-red Stone and Orange-red stone are composed of granulose or massive disseminated in the matrix. But red parts of Pomegranate-red Stone and Flower-red Stone are composed of dots or nervation disseminated in the matrix. In XRD tests, the main and minor mineral compositions had been studied, and the type of the stone had been decided. The main miner composition is pyrophyllite in Jelly Flower-red Stone, Flower-red Stone and Orange-red Stone. So they belong to Pyrophyllite-type Qingtian Stone. Pyrophyllite has two polymorphic types, which are 1Tc and 2M. According to the form and site of the diffraction peaks of XRD pattern at 19°~ 22° (2θ) and 28~31°(2θ), Jelly Flower-red Stone is mainly composed of 2M pyrophyllite, and a minor of 1Tc pyrophyllite. Flower-red Stone and Pomegranate-red Stone are mainly composed of 2M pyrophyllite. The minor compositions are dickite in Jelly Flower-red Stone, quartz in Flower-red Stone, muscovite in Pomegranate-red Stone, respectively. However, the main composition is dickite in Orange-red Stone, which belongs to Dickite-type Qingtian Stone. Dicket has order→disorder structure, which can be decided by XRD diffraction peaks at (020), (110), (112). The minor composition of Orange-red Stone is quartz. Minor and trace minerals in the red Qingtian Stones were tested by LRM. And LRM was mainly used to detect minerals at red parts, and to decide the color causation of red Qingtian Stones. The results indicate that all of the four red Qingtian Stones contain hematite. On the other hand, Jelly Flower-red Stone also contains hematite and pyrophyllite. Flower-red Stone also contains a lot of quartz and minor pyrophyllite and rutile. Pomegranate-red Stone also contains pyrophyllite and rutile. Orange-red Stone also contains quartz. Red color is caused by hematite in Jelly Flower-red Stone, Flower-red Stone and Orange-red Stone, but is caused by rutile in Pomegranate-red Stone. Therefore, all of the four studied Qingtian Stones are colored by impurity minerals.