关键词: 青田石, 交代变质作用, 次生石英岩, 浙江青田县

Abstract:

Petrologically, Qingtian stone is a kind of rock comprising clay mineral of pyrophyllites, which formed by hydrothermal metasomatism and metamorphism  and is a kind of secondary quartzite. The present work focuses on petrography, mineral composition and varieties of Qingtian stone, suggesting that hydrothermal metasomatism and metamorphism of intermediateacid volcanic rocks lead to the formation of the stone. Our investigations include petrographical observations, physical and chemical characteristics, geochemical compositions, field environments and reviews of previous papers of Qingtian stone. The studies show that Qingtian stone can be classified into several types, according to its main mineral components which are closely related to its protolith, features of the hydrothermal fluid, and temperature pressure conditions. Its color and quality are closely related to the mineral component, microstructure, and colorcausing cations. High quality Qingtian stone had undergone  extensive  metasomatism and metamorphism, whereas others with lower quality commonly had  undergone slight metasomatism and metamorphism. It is suggested that determination of alteration zone of volcanic rocks of Mesozoic and Cenozoic Era by means of geological mapping is an effective way of  looking for the high quality Qingtian stone, and  must be concerned in the identification and subsequent  evaluation of the stone.

Key words: Qingtian stone, metasomatic metamorphism, secondary quartzite;Qingtian County, Zhejiang Province