Rock IdentifierSandstone
Key takeaways
- Sandstone is a clastic sedimentary rock of cemented sand-sized grains.
- It feels gritty like sandpaper and often shows layers and cross-bedding.
- The cement (silica, calcite, iron oxide) sets its hardness and color.
What it is
Sandstone forms when sand — usually quartz grains — accumulates in dunes, beaches, or riverbeds and is buried, compacted, and glued together by mineral cement. It's one of the most widespread and recognizable sedimentary rocks, ranging from pale cream to deep rust red.
How to recognize it
Run a finger over it: sandstone feels gritty, like coarse sandpaper, and you can often see and feel the individual rounded grains. It frequently shows visible layering (bedding) and sometimes sweeping cross-beds recording ancient dunes or currents. Grains may rub off softer, poorly cemented examples.
Cement, color & look-alikes
The cement matters: silica-cemented sandstone is hard and durable, calcite-cemented sandstone fizzes in acid, and iron-oxide cement paints it red or orange. Pushed to metamorphism, sandstone fuses into quartzite — much harder, glassier, and breaking through grains rather than around them. If a 'sandstone' scratches glass and has lost its gritty feel, suspect quartzite.
