Intriguing minerals: corundum in the world of rubies and sapphires with special attention to Macedonian rubies

Abstract

This lecture text presents features of the fascinating mineral corundum and its gem varieties, ruby and sapphire. The geologic occurrences of its varieties and the best-known world localities are presented in detail. The mineralogy and crystallography of corundum, as well as its occurrence forms, are discussed. The origin of their colour varieties and their usage are described, in addition to their important physical characteristics. Applications in the watch and laser industries and as an abrasive material, among others, are included. The ruby variety from dolomite marble in North Macedonia exhibits the unique optical phenomenon known as diasporescence-the inclusion of diaspore crystals in the corundum matrix. This phenomenon affects the parting of corundum crystals and influences their colour, density and hardness. Therefore, special attention is paid here to morphological and physical characteristics of the Macedonian gem corundum.

Orange luminescence of α‐Al2O3 related to clusters consisting of F centers and divalent cations

“…F 2 ‐type centers are described as two nearest‐neighbor anion vacancies on adjacent basal planes [18]. However, a similar orange luminescence in nonirradiated samples, that is, natural or synthetic, has been mentioned several times but rarely studied or fully described [19–23]. Comparable luminescence was also observed in Be‐diffused crystals where it is present only in areas where the Be ion was detected using laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) [24, 25].…”