Quartz (SiO2) is a common mineral found in all three classes of rocks (igneous, metamorphic and sedimentary), in many environments and in a range of colours. However, rose and blue quartz are less common than some of the other varieties. This article discussed these two extraordinary minerals.
Rose quartz has a pale pink to rose-red colour, thought to be caused by trace amounts of titanium, which absorbs all colours except pink. In a laboratory experiment, samples of rose quartz from several localities were carefully dissolved in acid. The remaining insoluble residue consisted of thin microscopic fibres, which may also be responsible for the colour of rose quartz.
Well-formed rose quartz crystals are rarely found in nature, but when they are, they are generally found in massive chunks associated with pegmatites (Fig. 1). The term pegmatite refers to exceptionally coarse-grained crystalline granite. Since rose quartz is cloudy, it is not popular as a faceted gem, but it is commonly made into cabochons (Fig. 2), rounded into beads for necklaces or carved into various objects.
It has been named as South Dakota’s official state mineral. Here, rock hounds have a good chance of finding specimens ranging from shades of light pink to rose-red. Some rose quartzes from South Dakota also have a distinctive asterism, that is, a star-shaped display of light on the polished surface.
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