Identifying the quality of a jade raw stone mainly involves examining the various features that appear on its weathered crust, which can provide valuable clues about the internal characteristics of the stone. The following surface phenomena are commonly observed on jade stones:
1. "Xue" refers to the appearance of irregular patches or spots on the surface of the jade's outer shell, typically in shades of black, dark green, or gray. This is often associated with emerald green coloration and serves as a source of chromium ions. Xue may appear as green areas with black specks. The main mineral component of xue is alkaline hornblende, usually forming columnar or fibrous aggregates, appearing indigo or blue-black. It is often surrounded by pyroxene, especially in jadeite. There is usually a noticeable color contrast between the xue area and the surrounding material. If one side has many flaky patches while the other has small dots, it could indicate the presence of minerals like strontium inside. If only one side shows xue and the surface is clean, it may not affect the interior much. However, if xue appears on two or more sides, there might be internal impurities.
2. "Pine flower" refers to the green patterns seen on the surface of a jade stone, which may represent internal coloration or shallow green on the skin. These patterns are formed due to the stable distribution of coloring ions during mineralization. By observing the depth, density, and shape of these pine flowers, one can estimate how the color is distributed within the jade. A thick and bright pine flower suggests high value, while the absence of such patterns might mean little color inside. On the other hand, if there are many pine flowers on the skin, the color may be present internally or just on the surface. Whether the pine flower penetrates deep into the stone also helps determine the color quality.
3. "Mist" is a thin, fog-like layer found between the outer weathered crust and the inner jadeite. It results from metamorphic changes in the jadeite minerals. As the original jadeite undergoes temperature and pressure changes, new secondary minerals form around it, creating layers: the central part being the primary jadeite, the middle layer being secondary minerals, and the outermost being the weathered crust. These secondary minerals are mostly albite and nepheline. Mist can vary in thickness and color—white, yellow, black, or red. The presence and color of the mist offer insights into the original rock's properties. For example, red or yellow mist indicates high iron content, which darkens the emerald green. White mist suggests lower iron content and purer jadeite, often indicating higher quality.
4. "Huang" refers to the green bands visible on the weathered crust of jadeite. These bands appear as convex, zigzag lines on the surface, resembling the coils of a python. They serve as an indicator of color distribution within the jade. During diagenesis and mineralization, different generations of jadeite form, leading to variations in structure and hardness. Fine-grained, dense jadeite tends to resist weathering better than coarse-grained, loose parts. The green areas are generally more resistant, causing them to protrude and form these green bands. These bands are typically the result of post-diagenetic transformations, where stress-induced fractures allow hydrothermal fluids to introduce colored ions, creating the green zones. These zones then recrystallize under continued stress, forming dense, curved structures of jadeite.
Most jade stones have a weathered crust, known as the "leather crust," formed through geological processes. If the crust is rough and grainy, it’s called "sand skin." Sand skin can come in various colors, including white, yellow, iron-colored, and black. White sand skin often indicates no internal color, though some may show light green or purple with good transparency. Yellow sand skin might contain more green inside, but the color is usually uneven. Iron sand skin is typically thin and associated with high-quality jade. Darker black or green sand skins often suggest deeper green interiors, even emerald greens. However, black sandstone jade can be inconsistent—some may have black spots, others may be very dry or dirty. Lime skin is grayish-white and soft, easily brushed off with a metal brush. It is often composed of kaolin and usually indicates good internal quality. Water-washed stones have smooth, non-gritty skin, feeling soft to the touch. Their skin is thin, and they come in various colors like brown, cyan, or light yellow. Because their skin is so thin, light can pass through, making internal conditions easier to assess. Water pebbles are typically transported over long distances, leaving behind denser, finer jadeite, which is generally of better quality.
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