Lithic Sandstone

Lithic sandstone (also called lithic arenite or litharenite) is a sandstone in which the framework grains are dominated by fragments of older rocks — pieces of shale, basalt, chert, slate, or other lithologies — rather than individual quartz or feldspar crystals.

Because rock fragments are mechanically and chemically less durable than quartz, their abundance indicates that the sediment was eroded, transported, and buried quickly, before weathering could break the fragments down. This makes lithic sandstones a record of active, mountainous source areas.

They are typically darker, grayer, and "dirtier" looking than clean quartz sandstones, and they are very common in tectonically active basins.

Lithic sandstones form when erosion strips material from rapidly uplifting terrains — volcanic arcs, fold-thrust belts, and rising mountain ranges. Rivers and submarine currents carry the rock fragments only a short distance before deposition, so the unstable grains survive.

The sand accumulates in settings such as alluvial fans, river channels, deltas, and especially deep-marine turbidite fans. After burial, compaction and cementation by silica, calcite, or clay bind the grains into solid rock.

They are abundant in foreland basins and trench-related deposits worldwide, and their composition can be read to reconstruct the type of mountains that shed the sediment.

Look for a gray to brown, often dark and 'dirty' sandstone in which a hand lens reveals visible chips of other rocks — fine-grained dark fragments, chert, or slate pieces — rather than clear quartz alone.

The grains are usually sand-sized and may be angular to subrounded, reflecting limited transport. Compared with quartz arenite (clean, light, well-rounded quartz) and arkose (rich in pink feldspar), lithic sandstone is darker and more varied in grain type.

If abundant fine clay matrix is present it grades into a wacke or greywacke. Hardness depends on cement, but the lithic fragments and quartz make it generally tough and gritty.

Lithic sandstone is used mainly as a construction and dimension stone for building, paving, and fill where a durable, attractively variegated stone is wanted. Its toughness makes it serviceable, though clay-rich varieties weather faster.

Economically it is most important as a reservoir and source-area indicator in petroleum geology: geologists study its rock-fragment content to reconstruct ancient mountain belts and basin history (a field called provenance analysis).

It has no gem or metaphysical use. Some attractive varieties are cut as flagstone or used decoratively.