Green jadeite is commonly referred to as "Cui," while "Fei" refers to jadeite that exhibits a red hue. The most valuable green jade is rare and highly sought after, characterized by vibrant color, good transparency, and a natural, smooth texture. But how much do you really know about the "Fei" or twilight colors in jade?
1. Fei Jade Types
Fei jade is primarily composed of hard jade minerals and iron oxides. Its crystal structure can be medium-coarse, fine, or microscopic columnar aggregates. During crystallization, it often forms fibrous or granular textures.
2. Red and Brown Series – The Twilight Colors
Jade colors are typically divided into four main groups: red-brown, green, white, and purple. Among these, the red-brown series is known as "Fei." This category includes various shades such as red, reddish-brown, brown, yellowish-brown, light yellowish-brown, and yellow.
3. Fei Color and FeO Content
The color of jadeite is closely related to the trace amount of FeO (iron oxide) present. For example, semitransparent white jadeite usually has FeO levels between 0-0.05%, while green jadeite contains around 0.14% FeO. In contrast, red jadeite can have up to 1.25% FeO.
4. Fei Color and Iron-Bearing Minerals
The Fei color in jade is directly linked to iron-bearing minerals. These minerals are often found within the jade grains or along cleavage planes. Different iron minerals produce different hues—such as gem-red from water-fibrite, light brown-yellow from water-needle iron ore, and reddish-brown from fibrite.
5. Fei is a Result of Geological Processes
Fei color in jadeite results from specific geological conditions. The source of iron can be either primary or secondary. For instance, "Laoshan jade" is found in riverbeds and develops a red-brown outer layer due to long-term weathering. This shell is formed through secondary iron impregnation. Similarly, "Xinshan jade" often shows red-brown bands along rock fractures, also caused by secondary iron infiltration. In dense jadeite, Fei color is more likely due to primary iron enrichment during crystal transformation.
Iron minerals tend to accumulate in open fissures and intersections. Secondary iron solutions can create layered structures over time. Large cracks may allow wider iron penetration, but this often leads to a loose jade texture.
6. Rare and Valuable
Fei-colored jade is extremely rare, determined by unique geological factors. However, the market is flooded with Fei jade jewelry, many of which are artificially dyed. Dyeing enhances the appearance of low-color or variegated jade, but artificial color differs from natural ones. Natural Fei jade has high value and cannot be easily imitated. Some pieces may be falsely labeled as natural jade.
7. Natural Fei Characteristics
Natural Fei jade often appears as a reddish-brown shell, sometimes containing hornblende or fibrous hornblende. The color is irregular and uneven. In gravel, the Fei layer is usually 2-3 cm deep and gradually fades outward. Under a microscope, the Fei color tends to follow mineral grain boundaries without showing an arachnoid pattern. Oil immersion reveals that the color penetrates the crystal. Cracks often show deeper color on both sides, with no wax or polymer filling involved.
8. Artificial Fei Features
Artificial Fei is usually created using heat and chemical treatments, with compounds like iron nitrate or sulfate used as dyes. On jewelry, the color appears flat and unnatural, without any natural layering. The color doesn’t align with the rock’s structure and often shows a clear arachnoid effect under magnification. Cracks may appear intensely colored, with visible internal reflections and often accompanied by polymer filling in the same color.
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