摘要
台湾软玉形成于五万年前,系超镁铁岩变成的蛇纹岩经交代而成。软玉主要为普通软玉、猫眼玉和蜡光玉三种。比其它的软玉稍硬些,且硬度与闪光性都有方向性,并含数种矿物包裹体。其地球化学特征是含铬极高,并影响到软玉的颜色。
The carbon-14 dating indicates that formation of Taiwan nephrite could be as early as fifty thousand years ago. The nephrite occurrences are known over an north-south distance of 60km, but production has been mainly from Fentien nephrite belt which is approximately 10 km long by 3 km wide extending from the Chiakangchi in the south to the Paipoaochi in the north. The Taiwan nephrite can be classified as common,cat' a-eye,and waxy nephrites,with 100 Mg/(Mg+Fe+Mn) atomic ratios:85. 5—92. 2,density: 1. 96—3. 04,a:0. 975—0. 997nm,b:l. 794—1. 811nm,c:0. 511—0. 532nm,α—1. 602—1. 610,β:1.622—1. 628,γ:1.625—1. 635. The hardness rangs from 472 to 1 000±kg/mm^2 in Vickers hardness,equivalent to 5 — 7 of Mohs scale,the latter value being higer than any value ever reported for nephrite and tremolite. The tremolite fibers are arranged in some crystallographic orientations, with the c(001) face perpendlicular to the fibrous structure. Cat' s-eye phenomenon can be observed on a(100) and b(010),but cannot on c(001). Absorption is stronger on c than on other faces. Chromite, picotite, grossular, serpentine, and chalcopyrite are the common inclusions in the nephrite.
Because the nephrite occurs in the hanging walls and footwalls of serpentinite,and because the nephrite contains serpentine and chromite inclusions and has similar amounts of trace elements as the serpentinite,the Taiwan nephrite deposit is believed to be a metasomatic product of serpentinite derived from ultramafic rock. In addition,the bowenite,a yellowish green translucent serpentine,was minde in Taiwan and sold as nephrite.
Spectrographic analyses of 53 Taiwan nephrites show in average (μg/g),Co 36, Cr 1044, Cu 17, Mn 1346, Ni 647, V 10, and Ti 24. Eight serpentinite samples,which are associated with nephrite, contain similar anounts of these trace elements. White and green nephrites contain approximately the same amount of FeO. Cr and Ni are responsible for the emerald-green color of tremolite nephrite. Agreen-yellow index:T(510+520+530+540nm)/T(590+600+610+620nm) is proposed by L. P. Tan to judge the degree of the coloration of nephrite. The transmittance is high in cat' s-eye nephrite,medium in common nephrite,and low in waxy nephrite which is nearly subtanslucent to cryptocrystalline texture.
The minerals associated with the nephrite in Taiwan were studied by five methods. Olivine,antigorite, chrysotile, pycnochlorite, actinolite-tremolite, talc, brucite, diopside, magnesite, dolomite. calcite, aragonite,quartz,titanite,chromite,picotite,magnetite,pyrrhotite,pyrite and chalcopyrite were found in the serpentinite. Diopside, zoisite, clinozoisite, epidote, actinolite-tremolite, grossular, hydrogrossular, quartz, clinochlore, calcite, vesuvianite, chromite, picotite and ilmenite were found in the diopsidefels. Clinogoisite, quartz, actinolite, tremolite, muscovite, albite, calcite, diopside,graphite and sanidine were found in the metasediments.
出处
《矿物岩石》
CAS
CSCD
1992年第4期21-27,共7页
Mineralogy and Petrology
关键词
软玉
台湾
猫眼玉
蜡光玉
nephrite
cat's-eye
waxy
bowenite
green-yellow index
Taiwan
