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Rimstone
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<p>Rimstone, also called gours, is a type of <a href="/facts/Speleothem/mwwTnySG">speleothem</a> (cave formation) in the form of a stone dam. Rimstone is made up of <a href="/facts/Calcite/gKMHYQJo">calcite</a> and other minerals that build up in cave pools. The formation created, which looks like stairs, often extends into <a href="/facts/Flowstone/YLb1UNCo">flowstone</a> above or below the original rimstone. Often, rimstone is covered with small, micro-gours on horizontal surfaces. Rimstone basins may form terraces that extend over hundreds of feet, with single basins known up to 200 feet long from Tham Xe Biang Fai in Laos. </p>