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Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which refers to the size of a single crystal inside a particle or grain. A single grain can be composed of several crystals. Granular material can range from very small colloidal particles, through clay, silt, sand, and gravel, to boulders. ==Krumbein phi scale== Size ranges define limits of classes that are given names in the Wentworth scale (or Udden–Wentworth scale) used in the United States. The Krumbein ''phi'' (φ) scale, a modification of the Wentworth scale created by W. C. Krumbein〔 〕 in 1937, is a logarithmic scale computed by the equation : where : is the Krumbein phi scale, : is the diameter of the particle, and : is a reference diameter, equal to 1 mm (to make the equation dimensionally consistent). This equation can be rearranged to find diameter using φ: : In some schemes, gravel is anything larger than sand (comprising granule, pebble, cobble, and boulder in the table above). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Grain size」の詳細全文を読む スポンサード リンク
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