A few black aggregates of the very rare Mn mineral takanelite in a small pieces of white matrix from a locality in Texas (Marfa, Presidio County, Texas, United States of America). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Takanelite
Takanelite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Mn²⁺,Ca)₂ₓ(Mn⁴⁺)₁₋ₓO₂·0.7H₂O.
It crystallizes in the hexagonal crystal system.
Key properties: Mohs hardness 2.5–3; specific gravity 3.43; Brownish black to dark brown streak; Submetallic to dull luster; optically uniaxial.
IMA symbol Tkn, IMA status: approved, named in 1970.
Formed in the oxide zone of a bedded manganese deposit in metamorphosed cherts (Nomura mine, Japan); a secondary mineral derived from alteration of rhodochrosite in a manganese deposit (Janggun mine, South Korea).
It is found associated with Braunite, todorokite, halloysite, goethite, quartz (Nomura mine, Japan); nsutite, pyrolusite (Janggun mine, South Korea).
The mineral was named to honor Dr. Katsutoshi Takane (1899–1945), Professor of Mineralogy, Tohoku University, Sendai, Japan.