Calcareous stone

The Natural Stone Institute sorts natural stone by formation first, then by chemistry, and the chemical split is the one its care page ties to cleaners.

NSI groups natural stone into three geological classes by how it formed: sedimentary, metamorphic and igneous. Within each class, NSI says "stones in each category can be either Calcareous or Siliceous." Siliceous stone, composed mainly of silicates such as quartz, feldspar and mica, is "generally resistant to most acids found in kitchen settings, although acidic cleaners are still not recommended", because, NSI says, such stones may contain trace levels of acid-sensitive minerals. The compound calcium carbonate itself, and how it forms on concrete as calcium carbonate efflorescence, is a separate word with its own page.

NSI's care page defines the class but names no stone in it; NSI's consumer variety pages are where travertine and marble are described by their chemistry.

NSI's consumer variety page for limestone and travertine says "Limestone and travertine, like marble, are of a calcium carbonate base, and as such, are vulnerable to alteration by exposure to mild acids." Its marble page adds that the calcite crystal, marble's basic building block, "is vulnerable to attack by mild acids." Neither variety page uses the word calcareous. The link is the chemistry: the care page defines calcareous stone as "composed mainly of calcium carbonate", and the variety pages put limestone, travertine and marble on that base. How marble and travertine differ from each other for cleaning is its own question at marble versus travertine.

The care page turns that chemistry into one cleaning instruction.

For calcareous stone, NSI's instruction is mild, non-acidic cleaners, and it warns that products containing lemon, vinegar or other acids may dull or etch it; both lines are quoted in the travertine and marble card of the paver cleaning page's materials section. The dull mark itself is what NSI calls an etch. Whether an acid cleaner is ever permitted on travertine is answered directly at can travertine be cleaned with acid.

Whether a particular deck or step counts as calcareous is a question for the stone supplier, not a cleaner; the stones NSI's variety pages put on a calcium carbonate base are limestone, travertine and marble. It is a separate question from pressure: what NSI does and does not publish about washing travertine is covered at pressure washing travertine.

Calcareous stone is one entry in a longer paver-job vocabulary. A driveway's laying pattern carries its own name, such as running bond, and neither word tells you anything about the other.