THE FORMATION OF PRECIOUS OPAL: CLUES FROM THE OPALIZATION OF BONE
THE FORMATION OF PRECIOUS OPAL: CLUES FROM THE OPALIZATION OF BONE
复制标题
珍贵蛋白石的形成：来自骨蛋白化的线索
DOI：
10.3749/canmin.46.1.139
复制
发表时间：
2008
影响因子：
0.9
通讯作者：
J. Brugger
中科院分区：
文献类型：
--
作者：
Benjamath Pewkliang;A. Pring;J. Brugger
来自南澳大利亚Andamooka的乳白色龙骨（蛇颈龙）的组成和微观结构已被分析，并与来自南澳大利亚Coober Pedy北部相同地质构造的部分被镁质方解石取代的龙骨进行了比较。粉末x射线衍射分析表明，乳白色骨由蛋白石ag和石英组成。主微量元素XRF分析表明，它们基本上是纯SiO2 (88.59 ~ 92.69 wt%)，少量Al2O3 （2.02 ~ 4.41 wt%）和H2O （3.36 ~ 4.23 wt%）。乳白色后无生物成因磷灰石痕迹。相对于PAAS，蛋白石的所有微量元素都被耗尽了。在蛋白石形成过程中，骨微观结构的粗细细节被保留到单个骨的水平（约100 μm），但中央管和边界区域已经扩大并充满玉髓，这延迟了蛋白石的形成。这些化学和显微结构特征与乳化过程是镁方解石部分替代骨后的二次替代相一致。它们也与蛋白石首先在骨骼留下的小腔中形成凝胶相一致，而单个蛋白石球在凝胶中沉淀时生长。凝胶粘度的变化为蛋白石中颜色和斑纹的出现提供了一个现成的解释。澳大利亚蛋白石矿区的蛋白化是钙化后的二次过程，这一迹象与第三纪形成时代相一致。
The composition and microstructure of opalized saurian bones (Plesiosaur) from Andamooka, South Australia, have been analyzed and compared to saurian bones that have been partially replaced by magnesian calcite from the same geological formation, north of Coober Pedy, South Australia. Powder X-ray-diffraction analyses show that the opalized bones are composed of opal-AG and quartz. Major- and minor-element XRF analyses show that they are essentially pure SiO2 (88.59 to 92.69 wt%), with minor amounts of Al2O3 (2.02 to 4.41 wt%) and H2O (3.36 to 4.23 wt%). No traces of biogenic apatite remain after opalization. The opal is depleted in all trace elements relative to PAAS. During the formation of the opal, the coarser details of the bone microstructure have been preserved down to the level of the individual osteons (scale of around 100 μm), but the central canals and the boundary area have been enlarged and filled with chalcedony, which postdates opal formation. These chemical and microstructural features are consistent with the opalization process being a secondary replacement after partial replacement of the bone by magnesian calcite. They are also consistent with the opal forming first as a gel in the small cavities left by the osteons, and the individual opal spheres growing as they settle within the gel. Changes in the viscosity of the gel provide a ready explanation for the occurrence of color and potch banding in opals. The indication that opalization is a secondary process after calcification on the Australian opal fields is consistent with a Tertiary age for formation.