Calcareous rock
calcareous rock (noun, pl. calcareous rocks;ecology term,Substrate term) – a calcite (limestone), i. e., a rock consisting of calcium carbonate, generally with a high pH (pH > 7), usually (vigorously) bubbling when treated with a strong acid (e. g., 10% HCl). Note: In a strict sense the term calcareous only applies to rocks that consist of calcite, i. e., that are entirely composed of calcium carbonates. In contrast, calciferous rocks are not necessarily composed entirely of calcite but only contain calcium carbonate. This distinction is, however, rather academic, because there are hardly any natural rocks that are pure calcites. Thus essentially all calcites contain impurities of other minerals. The term calcareous rock is frequently used as opposed to siliceous rock even though siliceous rocks are not necessarily devoid of calcite, but may contain traces or even relatively large amounts of calcium carbonate. More accurately rocks devoid of any calcium carbonate should therefore be referred to as non-calciferous. The HCl-test frequently applied to detect calcium carbonate can be misleading if a rock contains magnesium carbonate that also shows a (weak) "bubbling" reaction.
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