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Macdonaldite

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Macdonaldite
White sprays of macdonaldite and blue botryoidal crust of mcguinnessite
General
CategoryPhyllosilicate
Formula
(repeating unit)		BaCa4Si16O36(OH)2·10H2O
IMA symbolMcd
Strunz classification9.EB.05
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupCmcm
Unit cella = 14.06 Å, b = 23.52 Å,
c = 13.08 Å; Z = 4
Identification
ColorColorless, white
Crystal habitAcicular also fibrous, in radiating aggregates; granular
Cleavage{010} perfect, {001} good, {100} indistinct
Mohs scale hardness3.5–4.0
LusterVitreous – silky
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.27
Optical propertiesBiaxial (+/−), surface relief – low,
Refractive indexnα = 1.518 nβ = 1.524 nγ = 1.530
Birefringence0.012
2V angleMeasured: 90°
DispersionWeak
References

Macdonaldite is a rare barium silicate mineral with a chemical formula of BaCa4Si16O36(OH)2·10H2O. Macdonaldite was first described in 1965 and named for Gordon A. Macdonald (1911–1978) an American volcanologist at the University of Hawaii.

Macdonaldite crystallises in the orthorhombic system. Macdonaldite is anisotropic with low relief.

Macdonaldite appears as veins and fracture coatings in a sanbornite 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. It has also been reported from a quarry in San Venanzo, Umbria, Italy.

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Mineralienatlas
  3. "Macdonaldite at webmineral.com".
  4. ^ "Macdonaldite at mindat.org".
  5. "Macdonaldite".
  6. Handbook of Mineralogy
  7. ^ 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.
  8. Bloss, F.D. (1999) Optical Crystallography. Mineralogical Society of America, 5, 161–163.


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