云南祖母绿的矿床地质及宝石学特征

云南祖母绿矿床产于寒武系变质岩中，矿体分别产于片麻岩的伟晶岩及云英岩脉中。属于典型的伟晶岩型或气成高温热液矿床。祖母绿的铬、钒来源于变质岩，而铍来源于伟晶岩。

GEMOLOGICAL CHARACTERISTICS AND DEPOSIT GEOLOGY OF YUNNAN EMERALD

Yunnan emerald deposit was found in (pre) Cambrian metamorphic rocks. Orebodies occur in two types of gneiss: (1) in pegmatites; (2)in greisen veins. It beIongs to classic-type pegmatite-type or pneumatolyte-hypothermal deposits. Elements V and Cr in emerald crystals come from metamorphic rocks and Be from pegmatites.Emerald crystals are mainly hexagonal prismatic. The terminations are usually flat faces joining the prism faces. Simple form { 1010} and { 0001 }, with a length of 10-200mm, and a diameter (D) of 5-50 mm. It is fresh green to yellowish green and bluish green.The crystals have obvious color zoning structure, and large quantities of fractures in the core,with deep-green, charming green, yel1owlsh-green and six-sided growth colored zoning in the outer layer of big crystal. Vanadium and chromium are main factors affecting the color. The Yunnanemerald contains 1. 5% V and 0. 06 % - 0. 20% Cr. From the center of crystals outward the content of V is relatively stable, but that 0f Cr increases gradually. There are four absorption peaks at 1 633, 3 594. 3 654 and 3 697 cm -1 in the infrared spectra, indicating that the emera1ds contain IItype crystal water and belong to high-alkali emeralds.Yupnan emeralds are characterized by the occurrence of natural inclusions such as tourmaline,arsenopyrite, V-bearing muscovite. feldspar and a large amount of gas-fluid phase inclusions