Sandstone

Learn about sandstone, a common clastic sedimentary rock.

Overview

Sandstone is a clastic sedimentary rock composed of sand-sized grains (0.0625-2mm) that have been cemented together. It forms from the accumulation and lithification of sand, typically in environments like beaches, deserts, rivers, and deltas. Sandstone is an important building stone.

What Is Sandstone?

Definition: Sandstone is a clastic sedimentary rock made of sand-sized mineral grains or rock fragments that have been cemented together. The grains are typically quartz, but can include feldspar, rock fragments, and other minerals. Composition: Primarily: - Quartz grains (most common) - Feldspar - Rock fragments - Cement (silica, calcite, or iron oxide) Color: Varies widely - white, tan, yellow, red, brown, gray - depending on cement and mineral content. Texture: Grain size 0.0625-2mm. Can be well-sorted (uniform grain size) or poorly sorted (mixed sizes).

Formation and Occurrence

How It Forms: 1. Sand accumulates in environments like beaches, deserts, rivers, or deltas 2. Over time, layers of sand are buried 3. Pressure and cementation turn the sand into rock Where It's Found: - Ancient beaches and shorelines - Desert sand dunes (now lithified) - River deposits - Delta deposits - Some marine environments Geological Settings: - Sedimentary basins - Areas of past deposition - Often interbedded with shale and other sedimentary rocks

Physical Properties

Hardness: 6-7 on Mohs scale (varies with cement type) Porosity: Can be very porous, making it a good reservoir rock for oil and gas. Weathering: Resistant to weathering, but can be friable (crumbly) if poorly cemented. Uses: - Building stone (very durable) - Paving stones - Glass manufacturing (high-purity quartz sandstone) - Abrasives - Oil and gas reservoirs

Varieties and Types

Quartz Sandstone (Quartzarenite): More than 90% quartz grains. Very pure. Arkose: Contains significant feldspar (25% or more). Often pink or reddish. Graywacke: Contains rock fragments and clay matrix. Dark gray to greenish. Lithic Sandstone: Contains significant rock fragments. Cross-Bedded Sandstone: Shows cross-bedding from dune or current deposition.

Rockhounding Value

Features to Look For: - Cross-bedding patterns - Ripple marks - Fossils (less common than in limestone) - Interesting colors and textures - Concretions Where to Look: - Quarries - Road cuts - Cliffs and outcrops - Areas with exposed sedimentary sequences What to Collect: - Specimens showing sedimentary structures - Interesting textures - Colorful varieties - Well-cemented specimens