基于现代测试技术的钠长石玉矿物组成研究

Research on Mineral Components of Albite Jade Base on Advanced Technology

虽然目前普遍认为钠长石玉的主要矿物组成是钠长石、阳起石、绿泥石、绿帘石、石英等,但仍有待验证。参照行业中对翡翠种的划分,将市场上常见的钠长石玉进行分类,通过偏光显微镜观察、电子探针测试、X射线粉末衍射仪等测试方法对钠长石玉的矿物组成进行了测试与分析,得出钠长石玉的主要组成矿物、次要矿物及副矿物。对一些学术著作中关于钠长石玉的矿物组成钠长石玉中"飘蓝花"品种的致色矿物是绿泥石和绿帘石提出质疑,结果表明,钠长石玉中"飘蓝花"矿物为绿辉石和角闪石。X射线粉末衍射试验的分析表明钠长石的有序度为1或非常接近1,为完全有序或非常接近完全有序的钠长石,说明钠长石玉的形成温度很低。

It is widely considered that albite jade is mainly composed of albite, actinolite, chlorite, epidote, quartz, jadeite,etc, However, in-depth analysis of mineral components in albite jade is lacking, and relative knowledge is incomprehensive. The gemmological charac teristics, mineral components, texture feature and degree of order of albite jade are studied in this paper. Refering to division of varieties in jadeite, the albite jade according to its base- ment and colour, can be classified into five kinds： （1） Icy-like albite jade; （2） Icy-like albite jade with ＂blue flower＂; （3） Green albite jade with white basement; （4） Cottonrose-like al- bite jade; （5） Dark-green albite jade, The minera! components of albite jade are studied by using many kinds of analytical methods, such as conventional gemmological methods, polari zing microscope, electron microprobe and X-ray powder diffraction. The results show that the refractive index of the albite jade is about 1.51--1.53（point measurement） and amphi bole part is about 1.63（point measurement）. The common colour of albite jade is colourless, white, green, grayish-green, yellow, brown, etc. None of the varieties have obvious ultra- violet fluorescence. The crystal morphologies of mineral under polarizing microscope are mainly hypidiomorphic or allotriomorphie granular, short prismatic and fibrous, and the tex tures are mainly the mylonitie and fibrous ranular crvstalloblastic textures_ Alhit~ albite jade often shows following structure types： tabular, foliaceous, isometric granular and sugar granular. Polysynthetic twin is common and twin lamellae is clear. The white veins or tinea spots in it are often composed of jadeite. The jadeite in colourless and transpar- ent albite jade presents white grains or masses and takes the shape of white foams, which is also white and granulous and short prismatic under polarizing microscope. Amphibole is found in the icy-like albite jade with ＂blue flower＂, dark green and green albite jade with white basement （＂Maw-sit sit＂ jade）, which is of dark-green phenocryst and light green fi- brous and long column. The slices of the samples are observed and 50 probe-testing points are circled, the ionic numbers are analyzed and calculated. For the calculation of crystal- chemical formulate, cationic method is used. Electronic valence balance（Fe3＋ , Fe2＋ ） is ap- plied to categorize pyroxene and amphibole. The main mineral component of Albite jade is al- bite and the accessory minerals are richterite, magnesiokatophorite, edenite,jadeite, omphacite and kosmochlor, with minor accessory strontium carbonate,chromite and hematite. This pa- per doubts that the minerals of ＂blue flower＂ in albite jade are chlorite and epidote. The au- thors confirm the minerals from those parts are omphacite and amphibole by means of EPMA and XRD. The results of XRD show that the order degree of albite is 1 or very close to 1, so the albite is completely ordered or very close to be fully ordered, which indicates that the formation temperature of albite jade is very low.