摘要
Lava and pyroclastic rock are main two sorts of volcanic rocks and represent two different eruptive types and petrogenic processes, so that they should be distinguished firstly for rock classification. Saccules have similar shapes and textures with fiammes, but are short of enough knowledge so far. Thus, Saccules-bearing rhyolitic—dacitic lavas are easily to be mistaken for fiamme-bearing welded tuffs, which results in wrong classifications between lava and pyroclastic rock. This paper first introduces distinctive characters of saccules and their differences from fiammes. Saccules, named after their overall shape, are composed of mineral aggregate (inner crystalline zone) and surrounding devitrified body (outer devitrified zone), usually stripped or lentiform with lacerated or whiskerlike ends, and also appear occasionally as patched extinction or devitrified fading body. They are formed by both fine crystallization of felsic high-temperature gas/liquid facies and devitrification of surrounding vitric components caused by the former’s heat releasing, which make up a primary texture in volcanic rocks. Identification between saccule and fiamme is helpful for accurate nomenclature and diagenesis of volcanic rocks, which can avoid broadening artificially the scope of pyroclastic rocks.
