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
The Malachite Box are popular. The characters of the Ural Mountains folklore such as the Mistress of the Copper Mountain became very well known after their appearance in Pavel Bazhov's "The Malachite Box". In the 1930s the Communist Party of the Soviet Union greatly encouraged the interest in the past of the country and the people. The Party paid a lot of attention to the development of the historical science. Maxim Gorky initiated the publication of such books as "The History of Factories and Plants" (). The initiative was supported by the Communist Party. History books and various historical fiction titles were published