Macdonaldite

{{Short description|Phyllosilicate mineral}} {{Infobox mineral | name = Macdonaldite | category = Phyllosilicate minerals | image = Macdonaldite-356329.jpg | imagesize = 260px | caption = White sprays of macdonaldite and blue botryoidal crust of mcguinnessite | formula = BaCa₄Si₁₆O₃₆(OH)₂·10H₂O | IMAsymbol = Mcd<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | strunz = 9.EB.05 | system = Orthorhombic | class = Dipyramidal (mmm) <br/>H-M symbol: (2/m 2/m 2/m) | symmetry = ''Cmcm'' | unit cell = a = 14.06&nbsp;Å, b = 23.52&nbsp;Å, <br/>c = 13.08&nbsp;Å; Z&nbsp;=&nbsp;4 | color = Colorless, white | habit = Acicular also fibrous, in radiating aggregates; granular | twinning = | cleavage = {010} perfect, {001} good, {100} indistinct | fracture = | tenacity = | mohs = 3.5–4.0 | luster = Vitreous – silky | refractive = n_α = 1.518 n_β = 1.524 n_γ = 1.530 | opticalprop = Biaxial (+/−), surface relief – low, | dispersion = Weak | birefringence = 0.012 | pleochroism = | 2V = Measured: 90° | streak = White | gravity = 2.27 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = | references = <ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Macdonaldite Mineralienatlas]</ref><ref>{{Cite web |url=http://webmineral.com/data/Macdonaldite.shtml |title=Macdonaldite at webmineral.com}}</ref><ref name=Mindat>{{Cite web |url=http://www.mindat.org/min-2506.html |title=Macdonaldite at mindat.org}}</ref><ref>{{Cite web |url=http://euromin.w3sites.net//mineraux/MACDONALDITE.html |title=Macdonaldite}}</ref><ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/macdonaldite.pdf Handbook of Mineralogy]</ref> }} '''Macdonaldite''' is a rare barium silicate mineral with a chemical formula of BaCa₄Si₁₆O₃₆(OH)₂·10H₂O.<ref name="multiple">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.</ref> Macdonaldite was first described in 1965 and named for Gordon A. Macdonald (1911–1978) an American volcanologist at the University of Hawaii.<ref name="multiple"/>

Macdonaldite crystallises in the orthorhombic system. Macdonaldite is anisotropic with low relief.<ref>Bloss, F.D. (1999) Optical Crystallography. Mineralogical Society of America, 5, 161–163.</ref>

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;<ref name=Mindat/><ref name="multiple"/> and from a quarry in San Venanzo, Umbria, Italy.<ref name=Mindat/>

==References== {{Reflist}}

Category:Barium minerals Category:Calcium minerals Category:Phyllosilicates Category:Orthorhombic minerals 10 Category:Minerals in space group 63 Category:Minerals described in 1965

{{silicate-mineral-stub}}