Gemological Characteristic Of “Trapiche” Ruby And Sapphire

"Trapiche" is a special growth phenomenon occurs in the gem minerals,sporadically seen in the ruby and sapphire.The single crystal is separated into six sectors by six arms and the center of the crystal might be a hexagonal core. The boundaries intersect in a central point or extend from the edge of a hexagonal central core.In this research,microscope,cathodoluminescence,electron microprobe,raman spectroscopy and scanning electron microscopy methods were applied to observe internal characteristics and have the components analysis of the representative samples of "trapiche" ruby and sapphire, and then have the further studies on the gem mineralogy characteristics.Dendritic arms in "trapiche" rubies are composed of directional tubes-like inclusions which act as the side branches concentrated at the locations, of crystal prisms,oriented perpendicular to crystal faces. The cores are having a texture similar to that of the arms. Arms of "trapiche" sapphire consists of vacancies formed in dislocation bundles and concentrated vertical to the crystal faces. While arms grow vertical to the prism faces. The existence of tubes and defects caused the relative density of "trapiche" rubies and sapphires to be lower than the standard values.The main area of "trapiche" ruby is relatively pure,composed of Al₂O₃,similar to non- "trapiche" rubies. Cores and arms are more activate for cathodoluminescence than ruby sectors,indicating that the tubes in the arm contained more inclusions and chromophorous elements. Based on the investigation by EDS,the tube-like inclusions in the arms contained elements of Al,Fe,Mg,Si,Ca,C,O,Zr,and inclusions are multiphase,consisted mainly of carbonate,silicate and oxide minerals. Raman spectroscopy reflected that dolomite, calcite, rutile,hematite,limonite are main inclusions in the arms. There are graphite and metal minerals, including iron and chromium element, observed in the core position.The distribution of trace-element contents and inclusions in these "trapiche" rubies is similar for marble-hosted rubies from Burma.Component analysis of "trapiche" sapphire by electron microsprobe and Ramanspectroscopy indicates that the composition of white arms is similar to blue sapphire sector,while the Raman absorption of white arms are more intensive than the blue sapphire sector. Therefore,the formation of "trapiche" texture in sapphire is caused to crystal structure instead of component difference.There are ilmenite,diaspore,iron oxides minerals inclusions in the cores. The species of inclusions that appeared in arms such as rutile and sapphirine are relevant to those in the core. Tube-like inclusions and calcite are only found occationally. The rutile and ilmenite have the high V content. Sapphirine were concentrated through the process of metamorphism and hydrated. liquid water was present in the directional white patches inclusions in the arms.The formation mechanism of "trapiche" ruby with arms and cores are dendritic growth,trapping the inclusions from the surrounding rocks during the rapid growth process result in the arms which are different to main part. Arms of "trapiche" sapphire formed related to defects and dislocations. An over growth may also be present.