The Mineral Composition of Jadeite: A Scientific Breakdown by Professor Michelle Au

Introduction

Jadeite, the most coveted gemstone in East Asian culture, derives its mesmerizing beauty and value from its complex mineral composition. Professor Michelle Au (歐陽秋眉), founder of the Hong Kong Gemmological Institute, revolutionized the understanding of jadeite by classifying its minerals into three genetic categories: metamorphic (crystalloblastic) minerals, primary minerals, and secondary minerals. This article distills her groundbreaking research, offering collectors and enthusiasts a clear guide to how mineralogy shapes jadeite’s color, texture, and market value.

1. Metamorphic Minerals: The Core of Jadeite

Over 50% of jadeite consists of pyroxene-group minerals, formed under high-pressure metamorphism:

Major Minerals (Dominant Pyroxenes)

Jadeite (NaAlSi₂O₆):
- The primary mineral in gem-quality jadeite.
- Color: Pure jadeite is colorless; traces of Cr³⁺ or Fe³⁺ substitute for Al³⁺, creating green hues.
- Structure: Short/long columnar or fibrous crystals (see Fig. 1).
Kosmochlor (NaCrSi₂O₆):
- Discovered terrestrially by Prof. Au in 1984.
- Color: Vibrant emerald-green (Fig. 3); key to “dry green” jadeite varieties.
- Forms exsolution textures with jadeite under low-temperature conditions.
Omphacite (Na-Ca-Mg-Fe pyroxene):
- Common in dark-green “black jadeite” (mo cui 墨翠).
- Chemistry: Transitional between jadeite and diopside (Na/(Na+Ca) = 0.2–0.8).

Minor Minerals (＜40%)

Amphiboles (e.g., actinolite, magnesio-riebeckite):
- Form via retrograde metamorphism, often replacing pyroxenes.
- Cause “blue flowers” (piao lan hua 飄藍花) or “black speckles” in lower-grade jadeite.
Feldspars (e.g., albite):
- Found in “water mozzi stone” (shui mo zi 水沫子), a jadeite simulant.

Accessory Minerals (Trace): Zircon, garnet, and apatite.

2. Primary & Secondary Minerals

Chromite (FeCr₂O₄):
A primary mineral providing Cr³⁺ for kosmochlor formation (Fig. 6).
Hydrothermal Minerals:
Molybdenite (MoS₂): Unique to Russian jadeite deposits.
Weathering Products:
Limonite/hematite: Cause yellow/red “skin” in rough jadeite.
Kaolinite: Forms from feldspar decomposition.

3. Key Implications for Collectors

Quality Indicators:

High-grade jadeite = jadeite + kosmochlor (vibrant green).
Low-grade jadeite = amphiboles + albite (mottled textures).

Authenticity: “Feit sui” (fake jade) often lacks pyroxene diversity.
Geographic Clues:

Burmese jadeite: Rich in kosmochlor.
Russian jadeite: Contains molybdenite.

Conclusion

Jadeite’s mineral complexity explains its aesthetic and economic diversity. As Prof. Au emphasizes, “Understanding these components is essential to appraising true value.” For deeper study, refer to her seminal works: Jadeite ABC (1997) and The Definition of Jadeite (1984).

Source: Ouyang, Q. (1999). “Mineral Component of Jadeite Jade.” Journal of Gems and Gemmology, 1(1), 18–26.

Omphacite jade under reflected (black) vs transmitted (green) light – Virtucasa Lab

翡翠的礦物組成：歐陽秋眉教授的科學解析

引言

翡翠，這種令東亞文化為之傾倒的寶石，其瑰麗色彩與價值源自複雜的礦物組成。香港珠寶學院創辦人歐陽秋眉教授將翡翠礦物分為三大成因類型：變質（變晶）礦物、原生礦物與次生礦物，徹底革新了學界認知。本文精煉她的關鍵研究，為藏家揭開礦物學如何決定翡翠的顏色、質地與市場價值。

1. 變質礦物：翡翠的核心

翡翠50%以上由輝石族礦物構成，形成於高壓變質環境：

主要礦物（輝石類）

硬玉（NaAlSi₂O₆）：
- 寶石級翡翠的主成分。
- 顏色：純硬玉無色；Cr³⁺或Fe³⁺替代Al³⁺時呈現綠色。
- 結構：短柱狀、纖維狀晶體（見圖版Ⅲ-1）。
鈉鉻輝石（NaCrSi₂O₆）：
- 歐陽教授於1984年首度在地殼中發現。
- 顏色：孔雀綠色（圖版Ⅲ-3），形成「乾青種」翡翠。
綠輝石（Na-Ca-Mg-Fe輝石）：
- 常見於「墨翠」，化學成分介於硬玉與透輝石之間。

次要礦物（＜40%）

角閃石（如陽起石、鎂鈉閃石）：
- 由退變質作用形成，常交代輝石，產生「飄藍花」或黑斑瑕疵。
長石（如鈉長石）：
- 見於仿翡翠的「水沫子」中。

副礦物：鋯石、石榴石等。

2. 原生與次生礦物

鉻鐵礦（FeCr₂O₄）：
提供鈉鉻輝石所需的鉻元素（圖版Ⅲ-6）。
熱液礦物：
輝鉬礦（MoS₂）：俄羅斯翡翠的特徵礦物。
風化產物：
褐鐵礦/赤鐵礦：形成翡翠原石的黃/紅色皮殼。
高嶺石：長石風化後的白色粉末。

3. 對收藏者的關鍵啟示

品質判據：

高檔翡翠 = 硬玉+鈉鉻輝石（鮮綠色）。
低檔翡翠 = 角閃石+鈉長石（雜質紋理）。

鑑偽要點：假翡翠（「B/C貨」）常缺乏輝石多樣性。
產地特徵：

緬甸翡翠：富含鈉鉻輝石。
俄羅斯翡翠：含輝鉬礦。

結語

翡翠的礦物多樣性，正是其美學與經濟價值的根基。如歐陽教授所言：「識得這些成分，方能辨玉之真諦。」欲深入研讀，請參考其著作《翡翠ABC》（1997）與《翡翠的定義》（1984）。

資料來源：歐陽秋眉（1999），〈翡翠的礦物組成〉，《寶石和寶石學雜誌》，1(1)，18–26。

The Mineral Composition of Jadeite: A Scientific Breakdown by Professor Michelle Au