Sandstone

Sandstone is an arenaceous sedimentary rock composed mainly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. Since sandstones often form highly visible cliffs and other rock formations, certain colors of sandstone may be strongly identified with certain regions. For instance, much of the North American West is well-known for its red sandstones.

Types of sandstone

Once the geological characteristics of a sandstone have been established, it can then be assigned to one of three broad groups:

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• arkosic sandstones, which have a high (>25%) feldspar content.
• quartzose sandstones which have a high (>90%) quartz content. Sometimes these sandstones are termed "orthoquartzites", e.g., the Tuscarora Quartzite of the Ridge-and-valley Appalachians.
• argillaceous sandstones, such as greywacke, which have a significant clay or silt content.