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spinel

(Encyclopedia)spinel, magnesium aluminum oxide, MgAl2O4, a mineral crystallizing in the isometric system, usually as octahedrons. It occurs as an accessory mineral in basic igneous rocks, in aluminum-rich metamorph...

Côte-d'Or

(Encyclopedia)Côte-d'Or kōt-dôr [key], department, E France, largely in Burgundy, partly in Champagne. ...

tourmaline

(Encyclopedia)tourmaline to͝orˈməlĭn, –lēn [key], complex borosilicate mineral with varying amounts of aluminum, iron, magnesium, sodium, lithium, potassium, and sometimes other elements, used as a gem. It o...

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...

whiting, powdery substance

(Encyclopedia)whiting, white, powdery substance, prepared by grinding chalk or some other source of calcium carbonate. When mixed with linseed oil it forms putty, and with water and several other substances it cons...

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...

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...