Specimens of blue calcite from Madagascar. Calcite is a common and widespread mineral with variable forms and colours, best recognised by its relatively low Mohs hardness (3) and its high reactivity with even weak acids: e.g. vinegar, along with its prominent cleavage in most varieties. It is possible that the blue colouration of this mineral is from copper impurities which often turns a hue of green or blue when it oxidises. These samples of blue calcite vary in colour from the typical light blue to a pale almost white, they are supplied in a card tray with an information label. These specimens are perfect for mineral collectors and ideal as a teaching aid.