Flower-Shaped Trapiche Ruby from Mong Hsu, Myanmar: A Revised Growth Mechanism

Two polished slices of flower-shaped trapiche ruby from Mong Hsu were analysed by X-ray computed tomography and X-ray micro-fluorescence. They are characterised by the presence of a core overgrown by two layers of ruby (with the outer one forming the 'petal' shape), and these three domains were previously attributed by Liu (2015) to a multi-stage growth mechanism. The present research indicates that these specimens show textural sector zoning associated with chemical sector zoning. In agreement with literature data, three different growth sectors are identified: a pinacoidal growth sector (corresponding to the core) and two sets of dipyramidal growth sectors with different inclinations with respect to the c-axis. The core, middle and outer layers are thus growth sectors of the same crystal, and no successive stages are needed to explain their formation. Therefore, the growth model proposed for other trapiche rubies from Myanmar also applies to the formation of these flower-shaped specimens. The distinctive shape of these rubies is due to weathering of the growth sectors and the sector boundaries.