Calcite Barely with copper penny Often used for optical prisms. Limestone and marble are varieties of calcite. A beautiful mineral occurring in many different colors. Chiefly used for making steel, it's also used in making opalescent glass, enameling cooking utensils and making hydrofluoric acid. Apatite Barely with knife blade Only one of the phosphate group to be considered a common mineral.
Greatest use is the source of phosphorus for most common fertilizers.
Used in manufacture of porcelain and as a source of aluminum in glass. The most common mineral, and often the most beautiful. Makes up sand on seashore, sandstone, quartzite. Some varieties are used as gemstones - crystal, amethyst, onyx, bloodstone, flint. Topaz Harder than other common materials Highly prized as a gem.