granular chert

granular chert . A compact, homogeneous, hard to soft chert, common in insoluble residues, composed of distinguishable and relatively uniform-sized grains, characterized by an uneven or rough fracture surface and by a dull to glimmering luster (Ireland et al., 1947, p.1486); it may appear saccharoidal. See also: granulated chert. Cf: smooth chert; chalky chert. Syn: crystalline chert.


melaphyre (mel'-a-phyre). A term originally applied to any dark-colored porphyritic igneous rock but later restricted to altered basalt, esp. of Carboniferous and Permian age. Obsolete.

directional drilling

directional drilling (di-rec'-tion-al). The intentional drilling of a well at controlled departures from the vertical and at controlled azimuths, often utilizing a whipstock or a special downhole assembly with a bent (angled) subassembly and a turbine motor located close to the drill bit. It is done to establish multiple wells from a single location such as an offshore platform, and for other purposes. Cf: deviation [drill]; sidetracking.


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