selbergite (sel'-berg-ite). A hypabyssal phonolite containing phenocrysts of leucite, nosean, sanidine, aegirine-augite, and biotite in a fine-grained groundmass of nepheline, alkali feldspar, and aegirine. The phenocrysts comprise a higher percentage of the volume of the rock than the groundmass. Its name, given by Brauns in 1922, is derived from Selberg, Laacher See district, Germany. The rock differs from schorenbergite in containing alkali feldspar. Obsolete.
GeoWord of the Day
The GeoWord of the Day is a free service of the American Geosciences Institute. All of the terms and definitions are from the Glossary of Geology, 5th Edition Revised.
rebulite (reb'-ul-ite). A submetallic gray monoclinic mineral: Tl5Sb5As8S22 .
pinnular (pin'-nu-lar). A plate forming part of a pinnule of a crinoid.
volkovskite (vol-kov'-skite). A colorless or pink triclinic monoclinic mineral: KCa4[B5O8(OH)]4[B(OH)3]4Cl•4H2O. .
bog expanse . The inner part of a raised bog within the rand. Cf: peat plateau.
knowe . A Scottish syn. of knoll.
molybdomenite (mo-lyb'-do-me-nite''). A colorless to yellowish-white monoclinic mineral: PbSe4+O3 .
tuff . Consolidated or cemented volcanic ash and lapilli. Not to be confused with tufa. Adj: tuffaceous.
urvantsevite (ur-vant'-sev-ite). A metallic hexagonal mineral: Pd(Bi,Pb)2 .
hogtuvaite . A subadamantine black triclinic mineral: (Ca,Na)2(Fe2+,Fe3+,Ti)6(Si,Be,Al)6O20. Syn: makarochkinite.
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