• journal_title：The Canadian Mineralogist
• Contributor：Lars Olov Andersson
• Publisher：Mineralogical Association of Canada
• Date：2013-02-01
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.51.1.15
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：51
• issue：1
• firstpage：15
• section：Article

The yellow color of beryl has been related to charge-transfer between Fe³⁺ ions substituting for octahedral Al³⁺ ions in the crystal and the surrounding oxygen ions. This assumption is contradicted by results from Electron Paramagnetic Resonance (EPR) measurements. A strong EPR signal from octahedral Fe³⁺ ions can be found in beryl of all colors and in colorless beryl. An EPR signal unique to yellow beryl comes from Fe³⁺ ions at a tetrahedral site. I propose that the yellow color of beryl comes from charge-transfer of tetrahedral Fe³⁺ ions. A simple model involving electrons trapped in the crystal structure explains the creation and the decay of the yellow color. The absence of trapped electrons in dark red beryl can explain the high temperature stability of its color. There is no evidence that iron ions are located in the channels of the beryl structure, which has often been assumed.