Hobbies And Interests
Chemical Background
Azurite has a rather complex chemical formula that is expressed as Cu3(CO3)2(OH)2. Azurite and malachite, a similar copper compound, are the only known minerals that form a copper carbonate mixture. However, since copper carbonate does not naturally exist in nature, the presence of a hydroxide molecule is necessary so that the copper can bond with the carbonate molecule.
Gemstone
The blue stone forms multiple, prismatic crystals that usually make for a showy and complex mineral. Azurite is popular both as a collectible mineral item and as a gem. However, the stone's susceptibility to heat, which turns the stone black, and to weather, which causes the mineral to change colors, limits its use as a gem.
Pigment
Another important historical use for azurite has been the use of this stone as a pigment in paint. This occurrence can be traced back to medieval and Renaissance times, when the stone was ground into a blue powder that was used to create a paint similar in color to ultramarine. Ultramarine pigments actually came from a much rarer mineral called lapis lazuli. However, modern day spectro-analysis of classical paintings seems to indicate that azurite was frequently used to produce a deep blue similar to ultramarine.
Weathering Process
When azurite is exposed to sunlight and moisture, it gradually changes to a similar compound called malachite. Malachite has a very similar chemical formula, Cu2(CO3)(OH)2, but a different color, green. This transformation is a result of oxidation, where the presence of water causes a slight chemical change that releases carbon dioxide and results in a new mineral compound with a slight difference in hue. This type of chemical change in the mineral world is very rare and not always detrimental, for the rich green color of malachite is very similar to the azurite blue.
Popular Varities
Several mineral varieties of azurite occur in nature, some of which are more highly valued than the blue variety. One of these is called "Bluebird," which is formed when azurite mixes with a dark red copper mineral called cuprite. Another interesting mineral combination is created when azurite replaces malachite. As a result, complex minerals are created that contain noticeable amounts of both minerals, resulting in a stunning blue and green patchwork of color. This rock is simply called azurite-malachite.