Matrix is the finer material in which larger particles are embedded. Lithic fragments are especially abundant in volcanic arc systems ( Stage E), but are common in most collision mountain buildings ( Stage F and Stage H). The exception to this is conglomerates and breccias. Frequently they are small, dark in color, and difficult or impossible to specifically identify in hand specimen. Lithic means 'rock' and all mechanically weathered pieces of another rock, or non-feldspar minerals weathered from a rock, are included here. Very simply, if a siliciclastic particle is not quartz or feldspar it is classified a lithic fragment. Rift systems ( Stage B and Stage C) frequently also have large amounts of feldspar. Sediments near high mountains frequently have large percentages of feldspar as batholiths and regional metamorphic rocks are uplifted and eroded (Wilson Cycle Stage F and Stage H). Medium to high grade metamorphic rocks also have large amounts of feldspar. calcium plagioclase in gabbro, and sodium plagioclase and orthoclase in granite. With only a few exceptions all igneous rocks have large amounts of feldspar e.g. Pure quartz sandstones form only under great tectonic stability when the land is not high enough for rocks to be exposed to weathering, such as during Wilson Cycle Stage A and Stage I.įeldspars are some of the most abundant minerals in the earth's crust. Usually quartz is mixed with one or more of the remaining three components. Since quartz, for all practical purposes, does not weather into anything else, and will remain after everything else is weathered or sorted out, it is one of the most important of the four components of sedimentary rock composition. You will learn to recognize and identify them as you study the rocks.ĬOMPONENTS OF SILICICLASTIC SEDIMENTARY ROCK COMPOSITION > Matrix (a catchall for the silt and clay grains that cannot be easily seen by eye).ĭescriptions of each category are below. > Lithic fragments (including rock fragments and mineral grains other than quartz) But in most cases rock composition can be defined by four compositional components: In addition, any incompletely weathered piece of igneous, sedimentary, or metamorphic rock can also be found in a sedimentary rock.Ī composition classification could become very complicated if all of these different particles were considered. After all, there are over 6000 known minerals. It might seem that an unlimited variety of particles could end up in a sedimentary rock. Thus, an arkose sandstone is a rock of sand sized particles, with a high percentage of those particles being feldspar. But any full rock name must specify both texture and composition. The basic classification only concerned texture, using the Wentworth size scale.

Sedimentary rocks are classified on the basis of the texture (grain size) of the rock, and composition.

Ternary diagram feldspar