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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...

intaglio

(Encyclopedia)intaglio ĭntălˈyō, –tälˈ– [key], design cut into stone or other material or etched or engraved in a metal plate, producing a concave, instead of a convex, effect. It is the reverse of a reli...

azurite

(Encyclopedia)azurite ăzhˈərīt [key], blue mineral, the basic carbonate of copper, occurring in monoclinic crystals or masses that range from transparent to translucent and opaque. It is usually associated with...

olivine

(Encyclopedia)olivine ŏlĭvˈēn [key], an iron-magnesium silicate mineral, (Mg,Fe)2SiO4, crystallizing in the orthorhombic system. It is a common constituent of magnesium-rich, silica-poor igneous rocks; metamorp...

Bras d'Or Lake

(Encyclopedia)Bras d'Or Lake brä dôr [key], arm of the Atlantic Ocean, c.360 sq mi (930 sq km), indenting deeply into Cape Breton Island, N.S., SE Canada, and occupying much of the interior. A narrow channel link...

rotation of crops

(Encyclopedia)rotation of crops, agricultural practice of varying the crops on a piece of land in a planned series, to save or increase the mineral or organic content of the soil, to increase crop yields, and to er...

Grignard reagent

(Encyclopedia)Grignard reagent grēnyärdˈ rēāˈjənt [key], any of an important class of extremely reactive chemical compounds used in the synthesis of hydrocarbons, alcohols, carboxylic acids, and other compou...

agar, substance obtained from seaweed

(Encyclopedia)agar äˈgär, āˈ–, ăgˈär [key], product obtained from several species of red algae, or seaweed, chiefly from the Ceylon, or Jaffna, moss (Gracilaria lichenoides) and species of Gelidium, harve...

fluorescence

(Encyclopedia)fluorescence flo͝orĕsˈəns [key], luminescence in which light of a visible color is emitted from a substance under stimulation or excitation by light or other forms of electromagnetic radiation or ...

caustic

(Encyclopedia)caustic, any strongly corrosive chemical substance, especially one that attacks organic matter. A caustic alkali is a metal hydroxide, especially that of an alkali metal; caustic soda is sodium hydrox...