166 Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones
From ore materials to precious gemstones, minerals play an important role in almost every aspect of our lives. This session will focus on characterization of economic minerals employing spectroscopic techniques, geochemical analysis, and microanalytical techniques.
Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 217A
Turquoise Terminology: Reviewing Major Element Chemistry of Global Turquoise Sources
Paper number: 166-8
Program: Technical Sessions
Time: 9:55 AM – 10:10 AM
Authors
Abstract
Turquoise is a copper-aluminum phosphate mineral and the naming member of the turquoise mineral group. The isostructural turquoise group consists of turquoise, planerite, faustite, aheylite, chalcosiderite, and an iron analogue (currently unnamed). X-ray diffraction and Raman spectroscopy are not always able to differentiate between turquoise group minerals because of their isostructural, micro- to cryptocrystalline, and heterogeneous nature. Most turquoise group analyses represent intermediate members of one or multiple solid-solution relationships; strict compositional boundaries for the use of the name “turquoise” have not been established. In this study, 30 turquoise samples from 16 localities were analyzed by LA-ICP-MS for major element concentrations to investigate the distribution of copper, iron, zinc, and other cations. CuO concentrations showed a broad range, from 1.71 – 9.64 wt.% (ideal turquoise = 9.78 wt.%, determined stoichiometrically). Fe2O3 was present in major element amounts in most samples (up to 7.61 wt.%), while only two natural samples had ZnO contents greater than 1.0 wt.%. The concentrations of divalent cations potentially filling the A-site were lower than expected, indicating vacancies characteristic of planerite. Iron commonly substituted for aluminum, though only two samples were iron-dominant at that site. Samples from two mines (Evans, Mexico, and Mona Lisa, Arkansas, USA) had intermediate compositions with average CuO below 5.0 wt.%. Boundary cases such as these demonstrate the practicality of the transitional term “planerite-turquoise” in a mineralogical setting, suggested for use when wt.% CuO is between 3.5 and 6.0 wt.%. In gemological and archaeological contexts, a broader use of “turquoise” is appropriate.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-412627
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