Minerals Review Ruby Deposits: a review and Geological Classification Gaston Giuliani
Figure 13. Solid and fluid inclusions trapped by trapiche rubies. (A
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| Figure 13. Solid and fluid inclusions trapped by trapiche rubies. (A) Primary fluid inclusions trapped
along the sector boundary of a trapiche ruby from Mong Hsu, Myanmar. The fluid inclusion was trapped within tube-like structures formed by dolomite (Dol). It is a multi-phase fluid inclusion containing a two-phase (liquid + vapor) CO 2 -H 2 S-S 8 -bearing fluid and minerals including diaspore (Dsp) and rutile (Rt). V = vapor phase, l = liquid phase; from [62]. Photo: Gaston Giuliani; (B) X-ray computed tomography image of a trapiche ruby from Luc Yen, north Vietnam, showing tube-like voids that contain solid and fluid inclusion cavities; from [57]. Photo: Christophe Morlot. In this geological context, the trapiche texture developed very quickly, as witnessed by the trapping of several solid and fluid inclusions and the formation of tube-like voids. The growth episodes in minerals are due to changes in the driving-force conditions [47]. In solution growth, mass transfer plays a key role. The driving force is defined by the difference in concentration between the bulk and subsurface supersaturation, i.e., the concentration gradient within the boundary layer [46]. Three growth episodes due to changes in driving force conditions were identified by [47] (Figure 14). Firstly, the core formed under low driving-force conditions via layer-by-layer growth (Step 1). Its development was hindered by the rapid formation of sector boundaries, which enveloped it and constitute the “skeleton” of the trapiche ruby (Step 2). These boundaries formed when the driving- force conditions increased and adhesive-type growth took place. Finally, a decrease in the driving- force conditions allowed the formation of growth sectors and the corresponding crystal faces through ordinary layer-by-layer growth (Step 3). The growth sectors filled the interstices left by the sector boundary, completing the trapiche texture. 3.3. Chemical Composition and Geographic Origin of Ruby Currently, the accurate chemical composition of rubies can be determined by several analytical techniques, such as X-ray fluorescence (XRF), electron microprobe analysis (EMPA), laser ablation- inductively coupled plasma-mass spectrometry (LA-ICP-MS), and secondary ion mass spectrometry (SIMS). Chemical data facilitate the differentiation between natural and synthetic rubies [67] (Figure 15) and help to determine their geological origin worldwide [11,68–72]. Baixar 8.58 Mb. Compartilhe com seus amigos:
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