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opal
(Encyclopedia)opal ōˈpəl [key], a mineral consisting of poorly crystalline to amorphous silica, SiO2·nH2O; the water content is quite variable but usually ranges from 3% to 10%. Common opal is usually colorless...fluorite
(Encyclopedia)fluorite flo͞oˈərspär [key], mineral appearing in various colors, e.g., green, yellow-brown, rose, and red. Chemically, it is calcium fluoride, CaF2. Its crystals, commonly cubic, are transparent ...agate
(Encyclopedia)agate ăgˈĭt [key], translucent, cryptocrystalline variety of quartz and a subvariety of chalcedony. Agates are identical in chemical structure to jasper, flint, chert, petrified wood, and tiger's-e...month
(Encyclopedia)month, in chronology, the conventional period of a lunation, i.e., passage of the moon through all its phases. It is usually computed at approximately 29 or 30 days. For the computation of the month a...silica
(Encyclopedia)silica or silicon dioxide, chemical compound, SiO2. It is insoluble in water, slightly soluble in alkalies, and soluble in dilute hydrofluoric acid. Pure silica is colorless to white. It occurs in sev...Black Lives Matter
(Encyclopedia)Black Lives Matter, a global political movement. Founded in 2013 by organizers Alicia Garza, Patrisse Cullors, and Opal Tometi, the #Black Lives Matter ...Brown, Trisha
(Encyclopedia)Brown, Trisha, 1936–2017, American dancer and choreographer acclaimed for having revolutionized modern dance in the late 20th cent., b. Aberdeen, Wash. After studying dance at Mills College (B.A., 1...gem, ornamental mineral or organic substance
(Encyclopedia)gem, commonly, a mineral or organic substance, cut and polished and used as an ornament. Gems also are used as seals (items of assurance) and as talismans (good-luck charms). For birthstones, see mont...hurricane
(Encyclopedia)CE5 View into the eye of a hurricane showing the structure of the surrounding cloud wall hurricane, tropical cyclone in which winds attain speeds greater than 74 mi (119 km) per hr. Wind speeds gu...Alabama, state, United States
(Encyclopedia)CE5 Alabama ăləbămˈə [key], state in the SE United States. It is bordered by Tennessee (N), Georgia (E), Florida and the Gulf of Mexico (S), and Mississippi (W). In 1954 the U.S. Supreme Co...Browse by Subject
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