TAIWAN CAT'S-EYE

Huang C.K., Yeh C.L.

doi:10.14915/gsjapan.5.4_157

The "Taiwan Cat's-Eye"is a tremolite cat's-eye. The gem material, cat's-eye tremolite occurs as veins at the contacts of graphite-sericite schist and serpentinite sills in association with nephrite, asbestus, talc and diopside-dominant skarn in the Fengtien area, south of Hualien. It is greenish yellow, pale yellow, honey yellow, green, rarely dark green, dark brown or black in color; translucent to opaque. H. 6-7, G. 3.045. Under the microscope, cat's-eye tremolite is colorless or pale green in color, consisting solely of fine, long sub-parallel fibers of tremolite in contrast to nephrite. Twisting or bending and wavy extinction are common. c∧Z' 0゜-10゜. α 1.613, β 1.626, γ 1.637 ; γ-α 0.24. The X-ray data are very similar to those of tremolite from St. Gotthard, Switzerland. Four chemical analyses reveal no marked differences in composition between the varieties of different colors, showing about 10% of the ferro-actinolite molecule. Some gemological features are also given. Diopside shows more crystal forms than previously reported, and the occurrence of grossularite is limited to diopside-grossularite veins near the contacts. Minor uvarovite and vesuvianite were first found in Taiwan. The former occuring as minute inclusions in diopside has n l. 778 and a_0 11.87A, corresponding to uvarovite with 10% Cr_2O_3. The latter of small prismatic crystals shows similarity in X- ray data to vesuvianite from Canzoccoli, Italy. The mineralization of the Fengtien nephrite-asbestus deposits may be divided into two stages : skarn formation and ore deposition, which might have taken place during serpentinitization by hydrothermal solutions rich in silica and lime. Cat's-eye tremolite was formed evidently later than nephrite.

TAIWAN CAT'S-EYE

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