Trithioarsenite, also called sulfarsenite, is the trianion . It is a pyramidal anion, as is typical of other compounds. It is generated by treatment of with a sulfide:
A fundamental synthetic trithioarsenite is , which features the pyramidal .
Thioarsenites are components of many sulfosalt minerals. An example is relatively common mineral proustite, , which is silver(I) trithioarsenite.