Orange Calcite

Hardness: 3 on Mohs scale (relatively soft). Color: Varies from pale orange to deep honey orange; can also be colorless, white, yellow, red, green, blue, brown, or black. Luster: Vitreous to resinous. Crystal Structure: Trigonal (rhombohedral). Cleavage: Perfect rhombohedral cleavage in three directions (often forming distinct rhombic shapes when broken). Specific Gravity: 2.71.

Calcite is a very common mineral formed in various geological environments. Orange calcite specifically gets its color from inclusions of iron. It forms in hydrothermal veins, stalactites, stalagmites, and other speleothem formations in caves, and as a component of sedimentary rocks like limestone and marble. Its formation can occur over millions of years through precipitation of calcium carbonate from water solutions. It is a primary component of many biological shells and skeletons and can also be found in igneous and metamorphic rocks.

Orange calcite is primarily used as an ornamental stone and in lapidary work for carvings, spheres, and tumbled stones due to its attractive color and ease of working. It is also used in crystal healing practices. Industrially, calcite (not necessarily orange) is a major component of cement and lime, used in agriculture to neutralize soil acidity, as a flux in metallurgy, and as an abrasive.

Calcite is the principal constituent of limestone and marble. It exhibits strong double refraction, meaning if you look through a clear piece of calcite at an image or text, it will appear doubled. The word "calcite" comes from Latin "calx" meaning lime. It is one of the most common minerals on Earth and can show fluorescence under ultraviolet light.

To identify orange calcite in the field, look for its distinctive orange color, relatively soft nature (it can be scratched with a penny), and its perfect rhombohedral cleavage which often results in broken pieces having distinct angled faces. It will also effervesce (fizz) vigorously when a drop of dilute hydrochloric acid is applied due to its carbonate composition. Common locations include Mexico, the USA (Missouri, Oklahoma), Brazil, and Peru. For collectors, it's sought after for its vibrant color and unique cleavage.