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topaz

(Encyclopedia)topaz tōˈpăz [key], aluminum silicate mineral with either hydroxyl radicals or fluorine, Al2SiO4(F,OH)2, used as a gem. It is commonly colorless or some shade of pale yellow to wine-yellow; pale bl...

hydrothermal vent

(Encyclopedia)hydrothermal vent, crack along a rift or ridge in the deep ocean floor that spews out water heated to high temperatures by the magma under the earth's crust. Some vents are in areas of seafloor spread...

cyanobacteria

(Encyclopedia)cyanobacteria sīˌənōbăktĭrˈēə, sī-ănˌō– [key] or blue-green algae, photosynthetic bacteria that contain chlorophyll. For many years they were classified in the plant kingdom along with ...

ocher

(Encyclopedia)ocher ōˈkər [key], mixture of varying proportions of iron oxide and clay, used as a pigment. It occurs naturally as yellow ocher (yellow or yellow-brown in color), the iron oxide being limonite, or...

Theiler, Max

(Encyclopedia)Theiler, Max mäks tīlˈər [key], 1899–1972, South African–American research physician, b. Pretoria, educated at the Univ. of Cape Town, St. Thomas's Hospital (London), and the London School of ...

black-eyed Susan

(Encyclopedia)black-eyed Susan or yellow daisy, North American daisylike wildflower (Rudbeckia hirta) of the family Asteraceae (aster family) with yellow rays and a dark brown center. It is a weedy biennial or annu...

Gorgas, William Crawford

(Encyclopedia)Gorgas, William Crawford, 1854–1920, American disease and sanitation expert, surgeon general of the United States, b. Mobile, Ala., grad. Bellevue Hospital Medical College, 1879. He served with the ...

shearwater

(Encyclopedia)shearwater, common name for members of the family Procellariidae, gull-like sea birds related to the petrel and the albatross and including the fulmar. Shearwaters are found on unfrozen saltwaters all...

buoy

(Encyclopedia)buoy boi, bo͞oˈē [key], float anchored in navigable waters to mark channels and indicate dangers to navigation (isolated rocks, mine fields, cables, and the like). The shape, color, number, and mar...

perch

(Encyclopedia)perch, common name for some members of the family Percidae, symmetrical freshwater fishes of N Europe, Asia, and North America. The perches belong to the large order Perciformes (spiny-finned fishes) ...