This is likely a local or descriptive term for a manganese-bearing pyroxene, not an officially recognized distinct mineral species. Its properties would depend on the specific pyroxene it refers to (e.g., if a Mn-rich Aegirine, then properties of Aegirine would apply).
(Likely Black, Brownish-Black, Greenish-Black)
Sphenomanganite is a fascinating mineral with unique geological characteristics. Detailed scientific information is often available through specialized mineralogical resources.
Comprehensive geological data for Sphenomanganite is currently being compiled. Please consult specialized mineralogical databases for detailed information.