Clastic (or detrital) rocks are made of clay, silt, sand, gravel, and/or boulders. These grains are usually made of silicate minerals (quartz, feldspar, mica, clay minerals, etc.) or rock fragments because most biochemical and chemical grains (see below) do not survive chemical weathering or extensive transport.

Clastic sedimentary rocks form from the accumulation and lithification of mechanical weathering debris. Examples include: breccia, conglomerate, sandstone, siltstone, and shale.

Clastic Texture Clastic rocks are named for their grain size and shape. Coarse-grained (>2 mm) rocks with rounded grains are called conglomerate. If the coarse-grains are angular, the rocks are called breccia. Conglomerates (left) are coarse-grained sedimentary rocks with rounded grains.

As we’ve seen in Chapter 5, most sand-sized clasts are made of quartz because quartz is more resistant to weathering than any other common mineral. Most clasts that are smaller than sand size (<1/16 mm) are made of clay minerals.

Clastic sedimentary rocks are made up of pieces of other rocks. For example, sand on a beach or in a dune can get buried. Under the pressure of burial, the sand is pressed together and compacted.

rocks that have been weathered, eroded, and deposited are called clastic rocks. Clasts are the fragments of rocks and minerals. Examples of clastic rocks are sandstone and mudstone. Non-clastic rocks are created when water evaporates or from the remains of plants and animals.

While marble can appear superficially similar to quartzite, a piece of marble will be able to be scratched by a metal blade, and marble will fizz on contact with dilute hydrochloric acid.

Marble is metamorphosed limestone. Limestone is a sedimentary rock that is composed of the mineral calcite.