Dendritic Opal

Hardness (Mohs): 5.5 - 6.5
Color: Colors vary from transparent to white, yellow, tan or green with black or brown inclusions.
Transparency: Translucent to Opaque
Notable Occurrences: Australia, Mexico, Turkey and United States

Dendritic Opal seems to be a generic term for opal from locations throughout the world which has dendritic inclusions, generally black fern-like or moss-like inclusions in a base of common opal (opal without play of color). The base opal can be anywhere from transparent to white, yellow, tan or green; and peruvian pink and blue opal is also sometimes referred to as "Dendritic Opal" when these inclusions are present. As with all opal, the common opal base is composed of spheres of silica surrounded by water and is therefore sensitive to extremes of heat and cold. It is helpful to keep stored in a cool (but not freezing) place, wrapped in a soft cloth (moistening the cloth can also help the preservation).