Description | This specimen of stibnite (with minor quartz) is 9 cm across and comes from an unknown location in Montana. Stibnite, Sb2S3 (antimony sulfide), is typically identified by its gray color and crystal clusters containing long curved crystals. When finer grained, it may be difficult to distinguish from other gray semimetallic minerals. Stibnite is the most important ore mineral for antimony (Sb), which is used in many industrial processes. |