Abstract
Relevance. It is known that minerals differ in morphology, features of the internal structure of crystals, chemical composition, etc., depending on the conditions of their formation and existence. These geochemical features of the gems crystallization are an important criterion for determining their deposit. In this paper, the impurity composition of the samples of emeralds from the deposits of Brazil, China, Zambia, Russia, Afghanistan, Colombia, and Tanzania was investigated by X-ray fluorescent analysis. The study of the impurity composition of emeralds by a non-destructive method and the construction of analytical dependences can be used as an additional way for determining the deposit of emeralds. Purpose of the work is the study of chemical composition of emeralds by X-ray fluorescent analysis to establish the relationship between the content of the main impurity elements and the deposit. Results. The data on the impurity composition of emeralds obtained by X-ray fluorescent analysis show that the content of impurities of Na, K, Rb, Cs, Mg, Fe, V, Cr differs from one deposit to another. The content of impurities of alkali metals and magnesium is higher in the samples from the shale-type deposits compared to the samples from deposits of the Colombian type. Thus, at the first stage, the type of deposit can be assumed. Further, the dependences plotted in the coordinate planes {Cr, V}, {Cs, Cr}, {Fe, Cr} show separate areas, delimited by the impurity ratios, which are typical for the samples from deposits in China, Colombia, Zambia, Afghanistan, and Tanzania. Conclusion. X-ray fluorescent analysis, as a non-destructive method for studying emeralds, is considered to be a promising approach to identifying their deposit, but as an additional method.
Highlights
There are two main geological and industrial types of emerald deposits
Purpose of this work is study of the chemical composition of emeralds by X-ray fluorescent analysis to establish the relationship between the content of the main impurity elements and the deposit, which can be used as an additional method for determining the emerald deposits
The content of impurities of some alkali metals and magnesium in emeralds differs depending on the deposit
Summary
There are two main geological and industrial types of emerald deposits. The first one is represented by carbonate-pyrite-albite-quartz veins in carbonaceous and calcareous schists [1, 2]. Sometimes they are formed in terrigenous-carbonate and sulfate-terrigenous-carbonate rocks [3]. The main large deposits are located in Colombia, so this region gave its name to one of the type of emeralds. Up to 75–80% of world production comes from deposits of this type. Objects of this type have a hydrothermal nature of formation. Typical inclusions in emeralds of the first type are the following ones: carbonaceous shales, halite and calcite crystals, grains of quartz, pyrite, and feldspar (albite)
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