Daim ntawv thov:Txhawm rau tshem tawm cov hlau impurities hauv cov txheej txheem ntub dej thiab ntxuav cov khoom tsis yog hlau, xws li quartz, sodium los yog potassium feldspar.Tsis tas li ntawd, nrog kev sib nqus sib nqus, nws muaj txiaj ntsig zoo heev hauv kev sib cais cov hlau nplaum uas tsis muaj zog, xws li hematite, specularite, limonite, siderite, manganese ore, thiab lwm yam.