Origins of Colour of Smithsonite from Yunnan, China

Abstract

Smithsonite exhibits an extensive range of colours in nature. The internal features, spectral characteristic, and trace elements of several coloured smithsonites (e.g., white, blue, blue-green, yellow, orange, and pink) from Lanping District, Yunnan Province, China, were analysed and the relationship between smithsonite colour and trace elements and/or impurities was discussed in this research. The presence of iron and manganese was closely associated with the yellow colour. Yellow greenockite grains scattered throughout parts of yellow smithsonites, ranging in size from sub-microscopic to 15 µm, efficiently changed the orange or yellow colour to “turkey fat” (a bright yellow variety of smithsonite resembling turkey fat in colour and botryoidal form) yellow. Pink colour in smithsonite was due to the presence of manganese ions. The main internal features in blue and blue-green samples were small interwoven acicular aurichalcite inclusions and alternating layers of aurichalcite–hemimorphite. Different proportions of the hole (CO3)− radicals, copper ions (nano-sized Cu-rich inclusions), and aurichalcite inclusions created green to blue coloration variations in smithsonite. The blue–green colour change was mainly caused by aurichalcite and hemimorphite, detected with a Raman test and chemical composition test.