Mineral Examples of such minerals are malachite (green) and azurite (blue). In contrast, allochromatic elements in minerals are present in trace amounts as impurities. An example of such a mineral would be the ruby and sapphire varieties of the mineral corundum. The colours of pseudochromatic minerals are the result of interference of light waves. Examples include labradorite and bornite. In addition to simple body colour, minerals can have various other distinctive optical properties, such as play of colours, asterism, chatoyancy, iridescence, tarnish, and pleochroism. Several of these properties involve variability in colour. Play of colour, such as in opal, results in
Italian submarine Malachite Spezia. In 1937 she undertook a training campaign near the Greek coast, in the Dodecanese and around Tobruk. During the Spanish Civil War, the submarine conducted a special mission between 24 August and 4 September 1937, and on August 29 she was subject to a anti-submarine search and attack. Between 1938 and 1940 "Malachite" was training and exercising for long periods around Tobruk. Upon her return to Italy, she was assigned to 47th Squadron (IV Submarine Group) based at Taranto. At the time of Italy's entrance into World War II, "Malachite" was reassigned to the X Submarine Group based at