CaCO3 in pearls consists of aragonite and calcite. The research shows that aragonite content directly affects the quality of pearls. As shown in table 9- 15, the relationship between the content and quality of aragonite in Hepu pearl.
Table 9- 15 Classification Table of Mineral Phase and Relative Quality of Hepu Pearl
(2) Crystallization habit: orthorhombic system (aragonite), calcite is triangular system. Fine crystals are arranged radially and have a concentric structure (Figure 9-23- 1).
(3) Hardness: 3.5 ~ 4.
(4) Relative density: 2.60 ~ 2.78, 2.83 ~ 2.86, often 2.85, and 2.73 ~ 2.85 for cultured pearls.
(5) Glossy: pearl luster, shell pearls do not show pearl luster.
(6) Luminescence: Under long-wave ultraviolet irradiation, most natural pearls appear light blue, light yellow, light green or light pink, while natural black pearls appear light pink to light red fluorescence, while artificially dyed black pearls often show inert or light white fluorescence.
(7) Color: pearls are rich in color, including white, milky white, milky yellow, pink, lilac purple, rose, gray, bronze, dark blue, blue-green and black.