Macdonaldite is a rare
barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
silicate mineral with a chemical formula of BaCa
4Si
16O
36(OH)
2·10H
2O.
[Alfors, J.T., Stinson, M.C., Matthews, R.A., and Pabst, A. (1965) Seven new barium minerals from eastern Fresno County, California. American Mineralogist, 50, 314-340.] Macdonaldite was first described in 1965 and named for
Gordon A. Macdonald
Gordon Andrew Macdonald (Boston, 15 October 1911 – Lanikai, 20 June 1978) was a notable American volcanologist. Macdonald was a Fellow of the Geological Society of America, the American Geophysical Union, the Mineralogical Society of America, a ...
(1911–1978) an American volcanologist at the
University of Hawaii.
Macdonaldite crystallises in the
orthorhombic
In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...
system. Macdonaldite is anisotropic with low relief.
[Bloss, F.D. (1999) Optical Crystallography. Mineralogical Society of America, 5, 161-163.]
Macdonaldite appears as
veins and fracture coatings in a
sanbornite
Sanbornite is a rare barium phyllosilicate mineral with formula Ba Si2 O5. Sanbornite is a colorless to white to pale green, platey orthorhombic mineral with Mohs hardness of 5 and a specific gravity of 3.74.
It was first described from Incli ...
and
quartz bearing
metamorphic rock. Macdonaldite was first described in 1965 for an occurrence near the Big Creek-Rush Creek area in
Fresno County, California. It has also been reported from
Mariposa and
Tulare counties in California.
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References
Barium minerals
Calcium minerals
Phyllosilicates
Orthorhombic minerals
Minerals in space group 63
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