Color Genesis and Compositional Characteristics of Color-Change Sapphire from Fuping, China

Abstract

The color-change sapphire occurs in sillimanite-biotite gneiss in Fuping County Hebei province, China, is one of most famous sapphire deposits in China. However, the color genesis, mechanisms of color changing and compositional characteristics of the sapphire remain enigmatic. In this contribution, the coloration in the Fuping sapphire, color changing mechanisms and, compositional characteristics were studied by conventional gemological instruments in conjunction with ultraviolet-visible spectroscopy and Laser ablation inductively coupled plasma mass spectrometer. The results show that the Fuping sapphire is characterized by purple-blue-to-purple-red changed effect and column-shaped, waist drum-shaped with higher degree of euhedral crystal. Reddish brown rutile inclusions with 120° crossed cleavage are commonly observed. The dominant coloring element of the Fuping sapphire is Fe3+, and subordinate elements are Fe2+, Cr3+ and V3+. The color-change effect is caused by trace elements Cr3+ and V3+. The chemical compositions of Fuping color-change sapphires are analogous to those of metamorphic blue sapphires. When geochemically compared with sapphires from Isalo/Ilakaka deposit in Madagascar, Ratnapura deposit in Sri Lanka and Mogok in Myanmar, the Fuping color-change sapphires have distinctly higher rare element contents of Fe, Cr and Ga.

Explaining Color Change in Gem-Quality Andradite Garnet

“…In gemology, the difference between the color of a gemstone in daylight and under incandescent light is called the alexandrite-like effect. Many gemstones naturally change color, such as alexandrite [6], spinel [7], sapphire [8], fluorite [9], and garnet [10]. The color-changing effect of gemstones is usually attributed to Cr 3+ and V 3+ , but there are exceptions.…”

Overview of Gemstone Resources in China

“…There are abundant inclusions, cracks, and partings in sapphire, leading to poor transparency. The primary inclusions are healing fractures, gas-liquid inclusions, and needle-like rutile [44]. Compared with metamorphism-related sapphires, the Fe and Ga concentration in Fuping sapphires is much higher, while the concentration of Ti is relatively lower.…”

“…Besides, the Changle sapphire shows an incomplete hexagonal zonation along the C-axis, forming a special trapiche sapphire [42]. LA-ICP-MS analysis [43,44] shows that sapphire in basalt is rich in Ti, Fe, and Ga but poor in Cr, whereas metamorphic sapphire is rich in Cr, poor in Fe, Ti, and Ga. The trace elements in the Changle sapphires contain Mg, Al, Si, Ti, V, Cr, Fe, Ga. And the Ga concentration (>100 ppm) in Changle sapphire is consistent with that of most other basalt-type sapphires [43].…”

“…Compared with metamorphism-related sapphires, the Fe and Ga concentration in Fuping sapphires is much higher, while the concentration of Ti is relatively lower. By comparing the contents of Cu and Ga in the Fuping sapphires are higher than sapphires from Madagascar, Burma, and Sri Lanka [43,44].…”

Genesis of Color Zonation and Chemical Composition of Penglai Sapphire in Hainan Province, China

“…The existence of trace elements in corundum is closely related to the geological background of their formation, so the study of their genesis provides important ways to interpret its formation history and identify specific origins [3,4]. Since metamorphic and basaltic sapphires have significant differences in trace elements, previous studies have proposed a variety of classification methods based on experimental data [5,6]. They found that trace elements such as Mg, Fe, Ti, Cr, Ga, and V and their ratios can well distinguish the origin and genesis of corundum.…”