Lithic fragment (geology)
Introduction '''Lithic fragments''', or '''lithics''', are pieces of other rocks that have been eroded down to sand size and now are sand grains in a sedimentary rock. They were first described and named (in their modern definitions) by Bill Dickinson in 1970.Lithic fragments can be derived from sedimentary, igneous or metamorphic rocks. A lithic fragment is defined using the Gazzi-Dickinson point-counting method and being in the sand-size fraction. Sand grains in sedimentary rocks that are fragments of larger rocks that are not identified using the Gazzi-Dickinson method are usually called rock fragments instead of lithic fragments. Sandstones rich in lithic fragments are called lithic sandstones.
Types ===Igneous (Lv)===These can include granular (~rhyolitic), microlitic (~andesitic), lathwork (~basaltic), and vitric (glassy). These correlations between composition and volcanic lithic fragment type are approximate, at best. By definition, intrusive igneous rock fragments can not be considered lithic fragments.===Sedimentary (Ls)===These can include shale siltstone fragments, and (at times) chert.===Metamorphic (Lm)===These can include fine-grained schist and phyllite fragments, among others.Image:LvMS-Lvg.jpg|Granular volcanic lithic fragment, scale in millimeters  Top picture in plane-polarized light, bottom picture in cross-polarized light.Image:LvMS-Lvm.jpg|Microlitic volcanic lithic fragment, scale in millimeters. Top picture in plane-polarized light, bottom picture in cross-polarized light.Image:LvMS-Lvl&Lvsm.jpg|Lathwork volcanic lithic fragment, scale in millimeters. Top picture in plane-polarized light, bottom picture in cross-polarized light.Image:LvMS-Lvv.jpg|Vitric volcanic lithic fragment, scale in millimeters. Top picture in plane-polarized light, bottom picture in cross-polarized light.
References