一串杂色手排的未知鉴定

Identification of An Unknown Variegated Bracelet

贝壳是一种常见的首饰的材料,其种类繁多,经常被加工或处理成各种形状的饰物,难以判断其原始种类。本次对一串疑似"贝壳"的杂色手排样品进行未知鉴定,并将它与市场上常见的贝壳首饰进行对比研究,了解市场上贝壳首饰的主要品类及基本特征。利用折射仪、静水称重法等方法对手排及其它贝壳饰品进行基本宝石学特征测试,采用X射线荧光光谱仪、X射线粉末衍射仪、傅里叶变换红外光谱仪、拉曼光谱仪对其成分及谱学特征进行测试,最后利用扫描电子显微镜对内部结构进行观察。经过测试和分析,得出手排成分为方解石,呈细长板片状排布,整体呈近似放射状分布,密度偏低,表面呈丝绢光泽,推测其取材于方解石型贝壳或贝壳方解石层。市场上的贝壳首饰主要矿物组成为文石,晶体呈砖墙状密集平行排布,它们的相对密度多高于手排样品,且表面显示珍珠光泽和晕彩。此外手排没有出现有机染料染色的特征,推测其颜色是由类胡萝卜素所致。

Shell is a kind of gem materials. There are many kinds of sh e l ls, which are usuallycut and treated to different ornaments. Therefore it is difficult to identify their original shapes. Recently, a special kind of brccelet was found in the market. It is made of fourteen rectangular be ad s, which have four kinds of colour： P u rp le , orange, pink paque and has a laminated s tru c tu re. The pink and orange part of bracelet and the bracelet has many things in common with shells. Therefore the study made compar-- son of the bracelet and other shell jewelr ies, which included Monetarmargaritifera , Pin c d a tama x ima , Trochus maculatus Linnaeus , Pteria penguin , etc. The fundamental gemmological characteristics of the bracelet and the other shell jewelries were tested by refractometer, balance, e tc , and the composition and spectral features were meas-ured by X-ray fluorescence spectrometer （XRF） , X-ray diffraction （XRD） , Fourier trans for-mation infrared spectrometer （FT IR ） and Raman spectrometer. The structure of the samples were analyzed by scanning electron microscope （SEM）. According to the te s t r e su l ts , the re-fractive index of the samples are all between 1. 530 and 1. 685 # and the average refractive in-dex of the sample is 1. 57. The average relative density of the sample is 2. 57, which is a li--tle lower than the other shell jewelries. It may be caused by the difference of composition andstructure , or by the influence of the hole on i t. They have similar are all rich inCa and Sr. They have completely different mineral composition and s tru c tu re. The bracelet is mainly made of calcite and it has a lath-like s tru c tu re. The calcite crystal was arranged radically and has a low relative density and silky lu s te r. The shell jewelries in themarket are mainly made of aragonite and have a brick-wall s t ru c tu re , which is almost fromnacre. The aragonite crystal was in parallel a r ran gem ent, which has highthan the unknown sample, and has pearl luster and iridescence. The bracelet dyed by organic dy es, and its colour may be caused by carotenoids according to Raman spcc-trum . In conclusion, the bracelet could be a kind of calcite-type shell or made from the cal-cite layer of a shell. The orange and pink colour may be directly caused by carotenoids, and the purple colour may be caused by carotenoids as well as protein complexation.