Natronambulite
Natronambulite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaMn²⁺₄Si₅O₁₄(OH).
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Rhodonite structural group.
Key properties: Mohs hardness 5.5–6; specific gravity 3.51; White, with slight orange tint streak; Vitreous luster; optically biaxial.
IMA symbol Nnbl, IMA status: approved, named in 1981.
Found in banded ore of a contact metamorphosed bedded manganese deposit, and as an accessory mineral in an albite-microcline-quartz pegmatite cutting the ore (Tanohata mine, Japan).
It is found associated with Aegirine, manganoan arfvedsonite, rhodonite, k^o zulite, marsturite, s¶erandite, quartz, albite, microcline (Tanohata mine, Japan); gypsum, brushite, cahnite.
The name refers to sodium, natrium, in its composition, and its relation to nambulite.