The Collaborative International Dictionary
Ullmannite
Ullmannite \Ull"mann*ite\, n. [So named after J. C. Ullman, a German chemist.] (Min.) A brittle mineral of a steel-gray color and metallic luster, containing antimony, arsenic, sulphur, and nickel.
Wiktionary
ullmannite
n. (context mineralogy English) A nickel antimony sulphide mineral.
Wikipedia
Ullmannite
Ullmannite is a nickel antimony sulfide mineral with formula: NiSbS. Considerable substitution occurs with cobalt and iron in the nickel site along with bismuth and arsenic in the antimony site. A solid solution series exists with the high cobalt willyamite.