Micro-World Gems & Gemology, Fall 2021, Vol. 57, No. 3

Fascinating Fluid Inclusions in Chinese Ruby

Fluid inclusion resembling a snake.
Figure 1. Fluid inclusion mimicking a snake in Yuanjiang ruby from China (left). The diagram on the right shows the details of this “snake.” Photomicrograph by Wenqing Huang; field of view 0.26 mm.

Gem rubies from the Yuanjiang deposit in Yunnan Province, China, host mineral inclusion assemblages comparable with those in rubies from other marble-hosted deposits (W.Q. Huang et al., “Trace element geochemistry and mineral inclusions constraints on the petrogenesis of a marble–hosted ruby deposit in Yunnan Province, China,” Canadian Mineralogist, Vol. 59, No. 2, 2021, pp. 381–408). Moreover, the fluid inclusion scenes in rubies from all of these deposits are also similar (G. Giuliani et al., “Fluid inclusions in ruby from Asian marble deposits: Genetic implications,” European Journal of Mineralogy, Vol. 27, No. 3, 2015, pp. 393–404).

Fluid inclusion resembling a fish.
Figure 2. This Yuanjiang ruby from China contains an interesting fish-like fluid inclusion. Photo­micrograph by Wenqing Huang; field of view 0.17 mm.

Two rubies from the Yuanjiang deposit showed several interesting fluid inclusions. The most impressive one strongly resembles a snake raising its head (figure 1). The other mimics a fish (figure 2). As shown in figures 1 and 2, the whole fluid cavity was split into two parts, both of which show a bubble. Raman spectroscopy analysis identified the transparent tabular crystals in the snake as diaspore (figure 1). The “snake” also hosted a solid inclusion of arsenopyrite (FeAsS); the needle on its head could not be characterized by Raman spectroscopy due to its fineness. The fluid composition was dominated by CO2 with minor components such as H2S, COS, and CH4, as revealed by Raman spectra and microthermometry. How these special inclusions formed has been speculated elsewhere (W.Q. Huang, “Fluid inclusion and titanite U–Pb age constraints on the Yuanjiang ruby mineralization in the Ailao Shan–Red River metamorphic belt, southwest China,” Canadian Mineralogist, 2021, accepted). This morphology-forming process has been explained by two mechanisms that evolved step by step. The first is morphological ripening that resulted in negative shapes of fluid inclusions; the second consists of subsequent reactions between the trapped H2O and the host corundum during the cooling of the inclusion, generating a diaspore that segregated the fluid completely.

Inclusions (mostly mineral inclusions) in gemstones that mimic scenery and landscapes are fascinating and relatively common. One novelty inclusion, an interesting “fried egg” of epigenetic residue trapped in a fissure, was recently found in rock crystal quartz (Fall 2020 G&G Micro-World, pp. 430–431). However, such novelty inclusions, especially fluid inclusions mimicking animals, are exceptionally rare.

Wenqing Huang (67019822@qq.com) is affiliated with the National Center of Supervision and Inspection on Quality of Gold and Silver Products at the Nanjing Institute of Product Quality Inspection in China.