Study on Gemmological Characteristics of Horny Gold Coral and Black Coral

The gemmological characteristics of the horny gold and black coral samples are studied by using the conventional testing methods,polarizing microscope,X-ray fluorescence spectrometer,grating spectrometer and infrared spectrometer.The results show that the refractive index of the samples is between 1.485 and 1.505,and the density is about 1.336~1.349 g/cm³.The cross section of the samples is of concentric ring structure and the vertical section being uneven thickness fiber structure,which could prove the transverse and vertical growth mechanism of the horny gold and black corals.The main chemical composition of the coral samples is pure organic matter,the main element is I,secondary elements are Cl,Br,S and Ba,and a small amount of Si,Ca,Mg,Na with trace elements Zn,Ti,Mn,Cu and V(but no Fe).The acid corrosion experiments show that the coral samples are insoluble in HCl and HNO₃,and slowly dissolve in H₂SO₄.The IR spectra of the samples are of weak—moderate—strong characteristic absorption peaks,which prove the existence of organic ingredients such as amino acid.