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Opoka |
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opoka [ō′päk·ə]
(petrology) A porous, flinty, and calcareous sedimentary rock, with conchoidal or irregular fracture, consisting of fine-grained opaline silica (up to 90%), and hardened by the presence of silica of organic origin. Opoka a tough, porous, flinty sedimentary rock. Opoka consists of up to 97 percent fine-grained hydrous amorphous silica, usually with admixtures of clay, sand, glauconite, and other substances. Poorly preserved remains of diatoms and sponge spicules are present. Opoka is distinguished from tripoli, which is similar in structure, by its greater uniformity and its conchoidal fracture. Its color ranges from light gray to dark gray and nearly black. Pure varieties of opoka have good adsorption properties. The Soviet scientist Ia. V. Samoilov, who introduced the term “opoka” into Russian geological literature in its modern meaning (1917), classifies opoka with rocks of organogenic origin; the American geologist W. H. Twenhofel and others classify it with rocks of chemogenic origin. Opoka is found primarily in Paleogene deposits and, to some extent, in Upper Cretaceous deposits. It is used in construction and as an adsorbent. Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content. |
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No references found | But if there is unsubtypable (UNSUBTYPABLE) H1N1 A influenza virus, the samples have to be sent to WHO designated laboratories for confirmation," Dr Martin Opoka, an epidemiologist with the EMRO said. The depth of gravel, sand, clay, peat, and dolomite quarries usually amounts to 6-12 m, that of limestone and opoka (gaize) - up to 15-20 m, only the deepest quarry where Triassic clay is extracted is as much as 50 m deep. Adam McGurk, Jonathan Hogg and Nathan Delfouneso were on target before Stephen Opoka scored a superb 30-yard consolation. |
Opoka |
OPNPA OPNS OPNV ÖPNV OPNZ Opo opo- OPOA OPOAA OPOB Opobalsam Opobalsamum Opobo OPOC OPOCE opocephalus Opochka OPOD Opodeldoc opodidymus OPODIS OPOE OPOET OPOH Opoka OpolOpolchenie Opole Opole Opole Wojewodztwo Opole Województwo Opolia Opolska Regionalna Organizacja Turystyczna Opolski Klub Motocykli Dawnych Opolski Osrodek Doradztwa Rolniczego Opolski Serwis Obrotu Nieruchomosciami Opolskie Centrum Demokracji Lokalnej Opolskie Przedsiebiorstwo Innowacyjno Wdrozeniowe Opolskiego Centrum Zdrowia Publicznego OPOM Opomyzidae Opone Opone OPONI Oponix Systems Inc. OPOO OPOP opopanax opopanax opopanaxes opopanaxes Opoponax Opoponax opoponaxes opoponaxes | |||||||
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