Pebble 314610 221858646 2008-06-26T12:06:30Z Hugo.arg 1456073 iw {{wiktionary}} [[Image:Wave Retreating from Pebbles.jpg|thumb|right|Sea wave polishing pebbles into rounded corners]] [[Image:Pebbles-oliv-e.jpg|thumb|right|Pebbles]] {{Otheruses}} A '''pebble''' is a [[clastic rocks|clast]] of [[rock (geology)|rock]] with a [[particle size]] of 4 to 64 [[millimeter]]s based on the [[Krumbein]] phi scale of [[sedimentology]]. It is generally described to be larger than [[gravel]] and smaller than [[cobble]]. A rock made predominantly of pebbles is termed a [[conglomerate (geology)|conglomerate]]. Pebble [[tools]] are among the earliest known man-made artifacts, dating from the [[Palaeolithic]] period of human history. They have been found at [[Olduvai Gorge]] (1.85 million years ago{{Fact|date=April 2007}}) and at [[Longuopo]] in [[China]] (1.8 to 1.5 MYA{{Fact|date=April 2007}}). A beach composed chiefly of surface pebbles is commonly termed a [[shingle beach]], which has [[armor (hydrology)|armoring characteristics]] with respect to wave [[erosion]]; moreover, this type of beach has unusual ecological niches that may provide [[habitat]] for a number of [[rare species|rare]] and [[endangered species]]. ==See also== * [[Gravel]] {{geol-stub}} [[Category:Sedimentology]] [[Category:Granular materials]] [[da:Ral (geologi)]] [[de:Kieselstein]] [[et:Veeris]] [[fr:Galet]] [[lt:Žvirgždas]] [[nl:Grind]] [[no:Rullestein]] [[pl:Otoczak (geologia)]] [[pt:Seixo (rocha)]] [[ru:Галька]] [[sv:Klapperstenar]]