Fluorite or fluorspar, 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 or...

, 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-eye, and are ...

Querétaro de Arteaga, state (1990 pop. 1,061,236), 4,432 sq mi (11,479 sq km), central Mexico. The city of Querétaro is the capital. With mountains in the north and valleys and plains in the s...

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...

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 occur...

Guanajuato, state (1990 pop. 3,982,593), 11,805 sq mi (30,575 sq km), W central Mexico, on the central plateau. The city of Guanajuato is the capital. The state's high average elevation (6,000...

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, ...

Alabama

Florida, state in the extreme SE United States. A long, low peninsula between the Atlantic Ocean (E) and the Gulf of Mexico (W), Florida is bordered by Georgia and Alabama (N). Area, 58,560 sq...