Abstract: Blue chalcedony is one of the most precious gemstones in Taiwan. The most popular imitations of blue chalcedony in Taiwan market are dyed chalcedony, dyed quartzite and blue opal. Recently we checked one of the new imitations and found its RI and SG very close to blue chalcedony but the spectrum of FTIR the same as glass. With the analysis of EDXRF we make sure it is a man-made glass.