Outstanding brown crystals of the extrememely rare Mn mineral holdawayite from the type locality in Kombat mine, Namibia. Originally, holdawayite is light to bright pink but it gradually changes to a brown color on exposure and in some cases has developed a thin black sooty coating that masks the true color. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Holdawayite
Holdawayite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Mn²⁺₆(CO₃)₂(OH)₇(Cl,OH).
It crystallizes in the monoclinic crystal system (space group C2/m).
Key properties: Mohs hardness 3; specific gravity 3.19; Pale pink streak; Vitreous, silky in fibrous aggregates luster; optically biaxial.
IMA symbol Hdw, IMA status: approved, named in 1986.
Locally abundant as a rare vein mineral in low-grade metamorphosed Mn-rich sedimentary rocks intercalated with sedimentary iron deposits.
It is found associated with Kutnohorite, ribbeite, alleghanyite, manganoan jacobsite, pyrochroite, sussexite, galena, copper, hydroxylapatite, calcian rhodochrosite, hematite, siderite.
The mineral was named to honor Dr. Michael Jon Holdaway (1936–), Professor of Petrology, Southern Methodist University, Dallas, Texas, USA.