This content was first published on IGR – Italian Gemological Review no. 22 in 2026. The information provided here is therefore current as of the original publication date.
A recent study published on Crystals in 2025, titled “Mineral Compositions and Organic Color-Related Compounds of Freshwater Bead-Cultured Pearls from Zhuji, Southeast China: Insights from Multi-Spectroscopic Analyses”, and conducted by Xi Li, Xiao-Yan Yu, and Cun Zhang, has provided new insights into the factors influencing the composition and color of freshwater bead-cultured pearls (FWBCPs) from Zhuji, one of the main pearl-producing areas in China’s Zhejiang Province.
The research, based on a multi-spectroscopic approach (FTIR, Raman, UV-Vis, CL, micro-FTIR, and TGA-DTA), analyzed twelve representative pearls and revealed that they are composed primarily of aragonite (93.2–94.5%), with approximately 5% organic matter and 0.3–0.7% adsorbed water. Vaterite was detected only in small quantities, localized near the nucleus or in regions of irregular growth. Raman analyses identified polyene compounds as the main natural colorants in the pearls. Characteristic Raman bands at 1525 cm−1 and 1131 cm−1 indicate that the color varies according to the conjugation length of the polyenes: shorter chains produce yellow-orange hues, whereas longer chains result in pink to violet shades.
UV-Vis spectra revealed a consistent absorption peak at 280.5 nm, attributed to conchiolin, along with broad absorption bands between 450 and 580 nm, whose position and intensity vary with the pearl color. No artificial pigments were detected, confirming the natural origin of the coloration.
A comparison with non-bead freshwater cultured pearls (FWNBCPs) showed that both types share similar mineral compositions and organic color-related compounds, but differ in internal structure, size, and density. FWBCPs tend to be larger and more spherical, while FWNBCPs are denser and more compact. The study emphasizes that the color of freshwater pearls is primarily determined by polyene-based organic compounds, whereas the mineral composition has little effect on hue or quality.
The study is available at this address: https://www.mdpi.com/2073-4352/15/9/824
Gem news published on IGR – Italian Gemological Review #22 – Spring 2026.
