*Article* **Gemological and Mineralogical Studies of Greenish Blue Apatite in Madagascar**

**Zhi-Yi Zhang, Bo Xu \*, Peng-Yu Yuan and Zi-Xuan Wang**

School of Gemmology, China University of Geosciences Beijing, 29 Xueyuan Road, Haidian District, Beijing 100083, China; 1009191124@cugb.edu.cn (Z.-Y.Z.); yuanpengyu@cugb.edu.cn (P.-Y.Y.); wangzx@cugb.edu.cn (Z.-X.W.)

**\*** Correspondence: bo.xu@cugb.edu.cn

**Abstract:** Madagascar is known as the 'Island of Gemstones' because it is full of gemstone resources. Apatite from Madagascar is widely popular because of its greenish blue Paraiba-like color. This study analyzes apatite from Madagascar through standard gemological characteristic methods, spectroscopic tests and chemical analyses (i.e., electron probe and laser ablation inductively coupled plasma mass spectrometry). This work explores the gemological and the diagenesis information recorded on Madagascar apatite by comparing them with apatite from other sources and establishes the origin information of Madagascar apatite. The origin characteristics are as follows: Apatite from Madagascar is fluorapatite, with excellent diaphaneity, greenish–blue color caused by Ce and Nd and crystal structure distortion indicated by spectroscopic tests. The F/Cl ratio (16.47 to 21.89) suggests its magmatic origin Cl loss during the weathering processes forming the source rocks, and lg fO2 (−10.30 to −10.35) reflects the high oxidation degree of magma.

**Keywords:** gemological; mineralogical; greenish blue apatite; fluorapatite
