General Information:
Chemical Formula:
Na(Fe++,Mg,Al)12(Si6O17)2(O,OH)10
Composition:
(Molecular Weight = 1,757.22 gm)
Sodium 1.31 % Na
Magnesium 2.77 % Mg
Aluminum 1.54 % Al
Iron 28.60 % Fe
Silicon 19.18 % Si
Hydrogen 0.17 % H
Oxygen 46.44 % O
Empirical Formula:
NaFe2+9Mg2Al2(Si6)2(O24)(OH)3
Environment:
In the Jurassic-aged Franciscan Formation metamorphosed to blue-shist facies (high pressure, low temperature ).
IMA Status:
Approved IMA 1966
Locality:
Laytonville quarry, 5 miles south of Laytonville, Mendocino Co. California.
Name Origin:
Named for Robert Andrew Howie (1923-), British mineralogist and petrologist, King's College, London University, UK.
Physical Properties:
Cleavage:
[010] Good, [100] Distinct
Color:
dark green or black.
Density:
3.378
Streak:
grayish black
More details...