A 2.4 by 2.2 cms fibrous mass. JSS specimen and photo. From: Laytonville Quarry, Laytonville, Coastal Range, Mendocino Co., California, USA. — Photo: John Sobolewski · CC BY 3.0
Howieite
Howieite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na(Fe²⁺,Fe³⁺,Al,Mg)₁₂(Si₆O₁₇)₂(O,OH)₁₀.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: specific gravity 3.378; Greasy luster; optically biaxial.
IMA symbol Hw, IMA status: approved, named in 1964.
An essential mineral in some of the metamorphosed shales, siliceous ironstones, and impure limestones of the Franciscan Formation (Laytonville district, California, USA).
It is found associated with Deerite, zussmanite, stilpnomelane, spessartine, riebeckite, quartz, aegirine, grunerite, aragonite, manganoan siderite.
The name refers to Professor Robert Andrew Howie (1923{), British mineralogist and petrologist, London University, London, England.