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Frequently-Used Geological Terms Part 44 Glossary Adapted from the Dictionary of Geological Terms L - Continued Low-Velocity Zone - 1. Weathered layer. 2. Zone in the upper mantle, variously defined as from 37 to 155 miles in depth, in which velocities are roughly 6% lower than in the outermost mantle, probably due to the near-melting-point temperature of the material. 3. A region inside the core boundary below a depth of 1800 miles, which produces a shadow zone at the earth’s surface. Low-Volatile Bituminous Coal - Bitu- minous coal, usually formed into a mass, containing 15-22% volatile matter, ana- lyzed on a dry, mineral-matter-free basis. It has over 15,000 BTU per pound (on a moist, mineral-matter-free basis). LPG - Liquefied petroleum gas. Lüders Lines - Planar deformation features, wider than ordinary shear fractures, inclined along planes of high shear stress, on which plastic or cataclastic defor- mation is concentrated. Luminescence - Emission of light by a substance which has received energy or electromagnetic radiation of a different wavelength from an external stimulus; also, the light produced. Luster - Reflection of light from the surface of a mineral, described by its quality and intensity; the appearance of a mineral in reflected light. Terms such as metal- lic or resinous refer to general appearance. Luster Mottling - 1. The shimmering appearance of a broken surface of a sand- stone cemented with calcite crystals a centimeter or more in diameter incorpo- rating colonies of detrital sand grains. 2. The macroscopic appearance of igneous rocks having small crystals of one mineral scattered irregularly in larger crystals of another mineral (poikilitic rocks). Lutaceous - Said of a sedimentary rock formed from mud; pertaining to a lutite. Also said of the texture of such a rock. Lutite - A general name for rocks com- posed of material that once was mud, e.g. shale, mudstone, calcilutite. Silicon has a blue-gray metallic luster. More terms to come next month! *1 .5 0 (+1! &2".6/ !$" +*2"*0&+* "*0". 0 (+1! %"!1(" 1*! 5 4%& &0+. "0 1, + .! +# &." 0+./ ""0&*$ *! +/,&0 (&05 +*! 5 ,! 0" *! ((%&*"5 " 01." . !" %+3 !&"/ .+$. ) ),(+5"" .+$. ) *-1"0 *! /&*+ &$%0 1"/! 5 ," '"./ *! ( //"/ **1 ( ""0&*$ /0 ."/&!"*0/ ""0&*$ *! &* ( + .! ""0&*$ "!*"/! 5 (1) &*$ "#."/%". +1./" +. )+." &*#+.) 0&+* 2&/&0 +1. " /&0" 333 )33 +.$ &**"/+0 0". "(( //+ & 0&+* 00% **1 ( . !" %+3 +*2"*0&+* 1-( 5-// "<67)06 1' "<67)06 1' $) %5) ()(-'%7)( 72 7,) :%7)5 :)// -1(8675< %576 /2'%7)( %1( 63%5)6 3529-()( *25 );-67-1+ )48-30)17 @ 527%5< 7%&/)6 12: 352(8')( :-7, /%5+) 5-1+ +)%5 %1( 3-1-21 ))( !)3%-56 !27%5< 7%&/)6 > 8( 38036 > %.25 '20321)176 21A7 *25+)7 5()5 <285 '23< 2* ?#5%16*)5 2* #)',12/2+<@ :5-77)1 &< 2,1 A 632-5 $ ,)67187 9) 1-( ,21) > %; ::: )1-((5-// '20 = ;'-7-1+ ',%1+)6= 54 NOVEMBER 2015 WorldWide Drilling Resource ®