Uvarovite* and Grossular from the Fengtien Nephrite Deposits, Eastern Taiwan

Hsien-Ming Wan and Chun-Lu Yeh
Mining Research and Service Organization, Industrial Technology Research Institute, 1 Tun Hwa South Road, Taipei 105, Taiwan
*[Editor's note added in proof. On the basis of the end-member molecules given in Table II the mineral described in this contribution as uvarovite is, in fact, chromian grossular.]

Abstract: Uvarovite and grossular, the former comparatively rare, occur along the serpentinite-graphite schist contact in the Fengtien area, on the eastern slope of the Central Range of Taiwan. Uvarovite occurs as small emerald-green euhedral crystals on diopside-fels with dodecahedral crystal forms and many other modifications. Its refractive index is 1.782, specific gravity 3.702, and unit cell edge 11.912 Å. Chemical and probe analyses give average Cr2O3 contents of 11.60 wt. %; spectrographic analysis shows significant enrichment in Cr, Be, Co, Y, Sb, and La over grossular. Associated minerals include nephrite, diopside, tremolite asbestos, zoisite, and clinozoisite. Grossular is reddish-brown; large crystals, dodecahedral in form often modified by trapezohedrons, are associated with diopside, idocrase, and calcite. n = 1.746, SG = 3.636, and a = 11.866 Å. Structurally and chemically it is quite near the grossular end member. Grossular is considered to be formed from pneumatolysis associated with the intrusion of ultramafic rocks, whereas uvarovite is a replacement product of relict chromite in the original ultramafic rocks where migration of elements such as silicon and calcium from wall rocks are prominent.

Mineralogical Magazine; March 1984 v. 48; no. 346; p. 31-37; DOI: 10.1180/minmag.1984.048.346.05
© 1984, The Mineralogical Society
Mineralogical Society (www.minersoc.org)