Calcite
Calcite is a chemical or biochemical mineral (biomineralization) composed of natural calcium carbonate (CaCO3), crystallizing in the rhombohedral system and main constituent of many sedimentary rocks: limestone, marl; it is one of the most abundant carbonates.
Calcite-colloid is a variety of colloidal calcite.
Color: pure calcite is white. The presence of cations other than calcium, and in particular transition metals, gives it an allochromatic coloring of yellow, orange, red, green, blue, brown, gray.
Luminescence: Mn2+ activates while Fe2+ suppresses the cathodoluminescence of calcite.
Classification controversy
Although calcite is classically described as rhombohedral, Massimo Nespolo, professor of mineralogy, states that it is more accurately trigonal with a rhombohedral lattice.
Calcite-colloid is a variety of colloidal calcite.
Color: pure calcite is white. The presence of cations other than calcium, and in particular transition metals, gives it an allochromatic coloring of yellow, orange, red, green, blue, brown, gray.
Luminescence: Mn2+ activates while Fe2+ suppresses the cathodoluminescence of calcite.
Classification controversy
Although calcite is classically described as rhombohedral, Massimo Nespolo, professor of mineralogy, states that it is more accurately trigonal with a rhombohedral lattice.