Anatase “Dandelion” in Agate
Rutile is a common inclusion in quartz, but its polymorphs, such as anatase and brookite, are much rarer to find. Recently, a spherical conglomeration of acicular anatase crystals (identified by Raman spectroscopy) resembling the seed-head phase of a dandelion was seen as an inclusion within an agate slice (see above). Nearby, orangy yellow iron staining was also observed in a dendritic growth pattern.
Anatase and rutile are both tetragonal crystallizations of titanium dioxide (TiO2). Rutile, with its more compact crystal structure, is more stable and therefore more common. Brookite and anatase will convert to rutile under specific heat and pressure conditions. Anatase typically manifests as reddish brown to brownish yellow tabular or pyramidal crystals. Anatase inclusions are rare, but this inclusion with an acicular crystal habit is an exceptionally unusual occurrence.
