Jadeite Texture Types & Their Geological Significance – Prof. Michelle Au’s Structural Analysis

Jadeite Texture Types & Their Geological Significance – Prof. Michelle Au’s Structural Analysis

Introduction

A jadeite’s value hinges not just on its color, but equally on its texture – the arrangement and interaction of its mineral crystals. Professor Michelle Au of the Hong Kong Gemmological Institute classifies jadeite textures into three genetic types: crystalloblastic, replacement, and cataclastic, each revealing distinct stages of the stone’s metamorphic history. This article deciphers her seminal research for collectors and gemology enthusiasts.

1. Texture Classification: The Three Genetic Types

1.1 Crystalloblastic Textures (Primary Metamorphism)

Formed during high-pressure metamorphism, these dominate jadeite’s structure:

Granoblastic: Short-columnar jadeite crystals (e.g., “bean seed” jade) with granular, interlocking grains.
Columnar/Fibrous: Fibrous jadeite (e.g., “glass seed”) indicates directional pressure during formation.
Porphyroblastic: Large “phenocrysts” (e.g., “ice-bean seed”) embedded in finer matrix.

Key Quality Indicator:

Fine-grained (0.1–0.5 mm) = Superior transparency (“water head”).
Coarse-grained (>2 mm) = Opaque, lower value.

1.2 Replacement Textures (Fluid Alteration)

Post-metamorphic fluid interactions create:

Edge Replacement: Mineral rims chemically altered (e.g., omphacite replacing jadeite edges).
Net Replacement: Kosmochlor forming web-like patterns in chromite (Fig. 5).
Pseudomorphism: Complete mineral replacement (e.g., kosmochlor mimicking chromite shapes).

1.3 Cataclastic Textures (Tectonic Stress)

Fractured: Cracked grains from mild stress.
Mylonitic: “Flow-like” patterns from deep crustal shearing.

2. Why Texture Matters

2.1 Practical Implications

Transparency: Fibrous textures (e.g., “老坑種”) scatter light less, enhancing brilliance.
Durability: Interlocked grains resist chipping.
Authenticity: Synthetic jade lacks natural replacement textures.

2.2 Geological Storytelling

Burmese Jadeite: High-pressure fibrous textures dominate.
Russian Jadeite: More fractured/cataclastic due to tectonic activity.

3. Key Takeaways for Collectors

Premium Grades: Seek fine-grained (<0.5 mm) or fibrous textures.
Avoid: Coarse “bean seed” or heavily fractured stones.
Geographic Clues: Replacement textures suggest Burmese origin; mylonitic textures may indicate Russian.

Source: Ouyang, Q. (2000). “Texture Types of Jadeite Jade and Its Genetic Implication.” Journal of Gems and Gemmology, 2(2), 1–6.

翡翠結構類型與地質意義——歐陽秋眉教授的權威解析

引言

翡翠的價值不僅取決於顏色，更與其結構（礦物晶體的排列方式）息息相關。香港珠寶學院歐陽秋眉教授將翡翠結構分為變晶結構、交代結構與碎裂結構三大成因類型，揭示翡翠漫長的地質演變歷程。本文為藏家解讀這項關鍵研究。

1. 結構分類：三大成因類型

1.1 變晶結構（主變質期）

形成於高壓變質環境，是翡翠的主體結構：

粒狀變晶：短柱狀硬玉晶體（如「豆種」），顆粒明顯。
柱狀/纖維狀：定向排列（如「玻璃種」）反映形成時的定向壓力。
斑狀變晶：粗大「斑晶」嵌於細粒基質中（如「冰豆種」）。

品質關鍵：

細粒（0.1–0.5毫米）= 高透明度（「水頭足」）。
粗粒（>2毫米）= 不透明，價值較低。

1.2 交代結構（流體作用）

後期熱液活動造成：

邊緣交代：礦物邊緣化學變化（如綠輝石取代硬玉外緣）。
網狀交代：鈉鉻輝石在鉻鐵礦中形成網格（圖版1-5）。
假象交代：礦物完全被取代（如鈉鉻輝石複製鉻鐵礦外形）。

1.3 碎裂結構（構造應力）

碎裂結構：礦物裂紋（輕微應力）。
糜稜結構：流動狀變形（深層地殼剪切）。

2. 結構的實際意義

2.1 鑑賞要點

透明度：纖維狀結構（如「老坑種」）光線散射少，更透亮。
耐久性：顆粒緊密結合者不易破损。
辨偽：合成翡翠缺乏天然交代紋理。

2.2 產地特徵

緬甸翡翠：以高壓纖維狀結構為主。
俄羅斯翡翠：因構造活動多碎裂紋理。

3. 給藏家的建議

優選：細粒（<0.5毫米）或纖維狀結構。
避開：粗粒「豆種」或裂隙多的翡翠。
產地判斷：交代結構多見於緬甸料；糜稜結構可能來自俄羅斯。

資料來源：歐陽秋眉（2000）。〈翡翠結構類型及其成因意義〉。《寶石和寶石學雜誌》，2(2)，1–6。

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Jadeite Texture Types & Their Geological Significance – Prof. Michelle Au’s Structural Analysis