How Do I Tell the Difference Between Crushed Coral & Sand?

Coral is the skeletons of marine animals. Living corals construct their hard parts from calcium carbonate, a mineral called calcite or aragonite. Sand is a term applied to fine grains of minerals, usually silicon dioxide, better known as quartz.

  1. Coral Properties

    • Whether calcite or aragonite, crushed or ground coral shares the same properties. The mineral is relatively soft. If grains are rubbed on a sheet of glass, the grains will break or powder. Calcite also effervesces in acids such as vinegar or hydrochloric acid. A few drops of acid will cause crushed coral to bubble like an overflowing soda. Some coral is actually a similar mineral, dolomite, which effervesces slowly unless powdered.

    Sand/Quartz Properties

    • Quartz sand is silica, a mineral that has almost the same hardness as glass. If grains of quartz sand are rubbed on plain glass, it is possible to scratch the glass. Quartz sand does not react to acids like calcite.

    Criteria

    • Test with acid first. Drip a little vinegar or diluted hydrochloric acid on the material. If it bubbles wildly, it's crushed coral. If it bubbles a little, use a magnifying glass. If all grains are bubbling a little, it's probably the dolomite form of coral. If only a few grains are bubbling, rub the material on plain glass -- rub hard. If the material scratches the glass, it's not coral.