Abstract：Further identifying the silica varieties and other minerals contained in the siliceous rocks of the Taiyuan formation,it is important to analyze its origin. By using the analytical methods of thin sections,scanning electron microscope,X-ray diffraction and differential thermal analysis,abundant pyrophyllite has been found rocks and opal has been confirmed as the main type of silica in the siliceous rocks at bottom of the Taiyuan Formation in Jiaozuo area. The new found pyrophyllite has typical optical character of pyrophyllite,clearly characteristic peak of X-ray diffraction,as well as the endothermic valleys of pyrophyllite in differential thermal curve. The pyrophyllite in the siliceous rocks is occurred in micro-fracture with two directions,and wrapped by opal.

Keyword：Taiyuan formation;siliceous rocks;pyrophyllite;opal;