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Open AccessArticle

Coexisting Rubies and Blue Sapphires from Major World Deposits: A Brief Review of Their Mineralogical Properties

Gemological Institute of America, 5355 Armada Drive, Carlsbad, CA 92008, USA
Minerals 2020, 10(5), 472; https://doi.org/10.3390/min10050472
Received: 3 March 2020 / Revised: 14 May 2020 / Accepted: 19 May 2020 / Published: 22 May 2020
(This article belongs to the Special Issue Mineralogy and Geochemistry of Ruby)
Gem corundum deposits are typically divided into blue sapphire and ruby deposits. However, this classification often overlooks the fact that the precious stones produced are the same mineral with only an overall slight difference in their trace element profiles. It can take only a couple thousand ppm chromium to create the rich, red color expected of a ruby. This contribution deals specifically with economically important gem corundum mining regions that produce both blue sapphires and rubies either in comparable quantities (Mogok, Myanmar, and the basalt-related gem fields on the border between Thailand and Cambodia at Chanthaburi, Thailand, and Pailin, Cambodia) or predominantly blue sapphires with rare rubies (secondary Montana sapphire deposits and Yogo Gulch in Montana as well as the gem fields of Sri Lanka). Comparison of the trace element profiles and inclusions in the blue sapphire/ruby assemblages in these deposits shows that there are both monogenetic and polygenetic assemblages in which the blue sapphires and rubies have the same geological origin (monogenetic) or distinct geological origins (polygenetic). In the monogenetic assemblages, the rubies and blue sapphires have essentially indistinguishable inclusions and trace element chemistry profiles (with the exception of Cr contents). On the other hand, polygenetic assemblages are composed of rubies and blue sapphires with distinct inclusions and trace element chemistry profiles. Notably, in the monogenetic assemblages, chromium seems to vary independently from other trace elements. In these assemblages, Cr can vary by nearly four orders of magnitude with essentially no consistent relationship to other trace elements. The observations described herein are an attempt to address the question of what the geochemical and geological constraints are that turn gem corundum into a spectacular ruby. View Full-Text
Keywords: corundum; ruby; sapphire; gemology; geology of gem deposits corundum; ruby; sapphire; gemology; geology of gem deposits
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Palke, A.C. Coexisting Rubies and Blue Sapphires from Major World Deposits: A Brief Review of Their Mineralogical Properties. Minerals 2020, 10, 472.

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