There had been no previous papers reporting the occurrence of arsenic in mercury ore in the form of simple mineral-native arsenic in China. In 1985, however, the a}.ithor discovered spherulitic native arsenic of hydrothermal orl- gin in the Bashan mercury deposit of Chadian area, Guizhou province, which is within the Hunan-Guizhou mercury ore belt. The native arsenic occurs in strongly silicified dolomitic 1imestone of Lo- wer Cambrian Qingxudong Formation(€31)and is associated with cinnabar and stibnite, The ore deposit displays obvious stratabound and hydrothermal trans- formation characteristics, and the near-ore wall rock alterations consist mainly of silicification,baritization, calcitization and pyritization, The native arsenic crystallized and precipitated at the early hydrothermal silicification stage. The native arsenic takes the grayish black spherulitic form, like pisolites for the larger ones and strawberry balls for the smaller ones, The tin-colored fresh fractures are liable to become dark in the air, The measured density of native arsenic Dm=5.61;Hvioog=115, Hv10g=120;Ro(Rg) -40.7(544nm). By using Dmax-IIIB diffractometer, it is determined that the native arsenic i5 of trigonal system, with ao=bo=3.761a，co=10.628A，a=β=90º，γ=120º. The d values of strong diffraction peaks include 3.517A(003)，2.767A(012)， 2.045A(104)，1.875A(110)，1.765A(006)and 1.554A(202)，and the main infra- red absorption spectral bands have wave number 800, 590, 475cm-1 etc. The electron microprobe analysis shows its chemical composition to be As=97.99一99.77, Sb=0.03-0.56, Hg=0.11-0.88 and S=0.09-40, suggesting that the spherulitic native arsenic is a pretty pure simple mineral.