The nano-grain sizes of the opaline matrix components in Anatolian fire opals

Reddish-orange and yellowish-white colored Anatolian fire opals from Turkey were investigated to reveal the nano-grain sizes of its opaline matrix components, such as opal-CT and opal-C silica building phases, using atomic force microscopy (AFM) before and after HF acid etching of the samples.Although the nano-grain sizes of the opaline matrix components of Anatolian fire opals had been obtained as about 23 nm with a graphical modeling of X-ray diffraction, the AFM micrographs demonstrate that the nano-grain sizes of the opaline matrix components of the reddish-orange and yellowish-white colored Anatolian fire opals have different values, both of which are lower than 23 nm. In the reddish-orange colored Anatolian fire opals, the nano-grain sizes of the opaline matrix components display a libration with a minimum of 759 pm and a maximum of 14.2 nm. In the yellowish-white colored Anatolian fire opals, the nano-grain sizes of the opaline matrix components display a libration with a minimum of 2.96 nm and a maximum of 13.6 nm. These grain sizes indicate that the smallest silica nanostructure among comparable fire opals around the world is present in the Miocene aged Anatolian fire opals of volcanic origin.