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Ulexite is an evaporate mineral and an ore of boron. It is formed during the evaporation of lake basins and occurs in white rounded crystalline masses. It is a hydrous borate of lime and soda and has a relative hardness of 2. Ulexite was named in honour of George Ulex, the German chemist who in 1850 first correctly analysed the mineral. One transparent variety of ulexite exhibits the rare property of transmitting light unaltered from one end of its crystals to the other.
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Ullmannite, named after J. C. Ullman, the German chemist, is a brittle mineral of a steel-grey colour and metallic lustre, containing antimony, arsenic, sulphur, and nickel.
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Umber is a naturally occurring mineral used as a pigment.
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In geology unconformability describes a want of parallelism between one series of strata and another, especially when it is due to a disturbance of the position of the earlier strata before the latter were deposited.
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In geology, unconformity describes a want of parallelism between strata in contact. With some authors unconformity is equivalent to unconformability; but it is often used more broadly, for example, to include the case when the parallelism of strata once conformable has been disturbed by faulting and the like.
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Underclay is a stratum of clay lying beneath a coal bed, often containing the roots of coal plants, especially the Stigmaria.
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In geology, unstratified describes rocks which are tot stratified, and is applied to massive rocks, such as granite, porphyry, etc., and also to deposits of loose material, such as the glacial till, which occur in masses without layers or strata.
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In geology an uplift is a raising or upheaval of strata so as to disturb their regularity and uniformity, and to occasion folds, dislocations, and the like.
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Uralite, so called because it was first observed in the Ural Mountains, is an amphibole resulting from the alternation of pyroxene by paramorphism. It is not uncommon in massive eruptive rocks. Uralite is green in colour.
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Uralitization is the change of pyroxene to amphibole by paramorphism.
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Uraninite is a radioactive important source of uranium. It consists chiefly of uranium oxide with some lead, thorium, etc. It occurs in pegmatites and veins in granite; also as sedimentary deposits. It is found in black octahedrons and also in masses with a pitch like lustre. It has a relative hardness of 6.
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Utica is a subdivision of the Trenton Period of the Lower Silurian, characterized in the State of New York by beds of shale.
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Abbreviations
Rocks & Minerals
