Gemmological and Spectral Characteristics of Emerald from Panjsher Valley, Afghanistan

Quality and origin are important factors affecting the price of emerald. Emeralds from different origins have their own gemmological characteristics, which are important basis to trace their hometown. This study takes the emerald samples from the Panjshir mining area in Afghanistan as the research objects, and uses large-scale instruments such as optical microscopy, infrared spectroscopy, micro ultraviolet visible near-infrared spectroscopy, Raman spectroscopy, etc. to conduct study on their gemmological characteristics, internal inclusion characteristics, chemical compositions, and colour genesis. The colour of emerald samples from Afghanistan is light green to dark green, and the common crystal form is hexagonal short columnar or tabular crystal. Black and brown associated minerals can be seen outside. Under the Charles filter, all except a few samples showed localized redness. The main inclusions of emerald samples from Afghanistan are long needle-like, shuttle-like or long tube-like multiphase fluid inclusions containing rock salt and potassium salt and solid mineral inclusions. Raman spectrum tests on inclusions found that the liquid component of multiphase inclusions in emerald samples from Afghanistan is mostly H₂O, and the solid component is mostly calcite and hematite. In addition, mineral inclusions contained in emerald are mainly composed of hematite, calcite, amorphous carbon, quartz, carbonaceous, apatite, etc. LA-ICP-MS was used to test the chemical compositions of the emerald samples from Afghanistan, the result indicated that the main chemical compositions of the emerald samples are BeO, Al₂O₃, SiO₂, and trace elements including Ca, Mg, Ti, Li, Na, K, Rb, Cs, Cr, V. Through infrared spectroscopy test, it is known that emerald from Afghanistans contain typeⅠand typeⅡwater, and the infrared absorption peak intensity of type Ⅱ water is greater than that of typeⅠwater, indicating that emerald samples from Afghanistans are mainly composed of type Ⅱ water. The alkali metal content in general beryl (and emerald) is positively correlated with type Ⅱ water content. The infrared test results mainly show type Ⅱ water, which is consistent with the high alkali metal content in LA-ICP-MS test results. The UV visible spectrum tests show that Cr³⁺ and V³⁺ are the chromogenic ions of emerald from Afghanistan. The gemmological, spectral and chemical composition characteristics of emeralds samples from Afghanistan will provide the basis for tracing their origin.