The Upper Jurassic porphyroclastic lava exposed in Xiangshan area, Jiangxi Province，usually contains certain amounts of almandite and andalusite which crystallized from magma as accessory constituents. Geochemically, it shows many characteristics of S-type volcanic rocks and has Nd, Sr, O iso- topic compositions. Optical and X-ray powder diffraction determinations indicate that the K-feldspar in porphyroclastic lava is mainly high orthoclase or low sanidine, with optic angles (-2V) ranging from 40ºto 53º,All occupancies at t1 9O)sites from 0.36 to 0.38 and degree of order δ' from -0.32 to 0.11. It is seen under TEM that exsolved fine albite lamellae are formed by the decom-position process of coherent spinodal with the compositional wave-length about 50一10pnm, whereas wide albite lamellae are formed by strain-free exsolution with lamella width some 50-200 nm. These data suggest that the Xiangshan porphyroclastic lava was formed in environment rather than plutonic environment. seen under TEM thatposition process of coherent spinodal with‘ the compositio3zal wave-length . than plutonic envi.roumeut. was volcanic environment rather