Dendritic Agate (or Dendritic Opal)

Hardness: 6.5-7 on Mohs scale (Agate), 5.5-6.5 (Opal); Color: Translucent to opaque white, gray, brown, or colorless with black or brown dendritic inclusions; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (Agate), Amorphous (Opal); Cleavage: None; Specific gravity: 2.58-2.64 (Agate), 1.98-2.25 (Opal)

Dendritic Agate forms in volcanic and metamorphic rocks. It's a silicon dioxide mineral, a variety of chalcedony, characterized by tree-like or fern-like inclusions of manganese or iron oxides, which crystallize within the agate or opal as they form in fractures and cavities. These dendrites are not fossilized plant material but mineral intrusions. Geological age varies widely depending on the host rock formation.

Primarily used in jewelry, cabochons, and ornamental carvings due to its unique and attractive patterns. It's also a popular collector's stone.

Dendritic Agate is often referred to as 'Picture Agate' because its inclusions can resemble miniature scenes, landscapes, or trees. The fern-like patterns are formed by hydrous iron and manganese oxides that grew within the agate. Despite their organic appearance, they are purely mineralogical formations.

Look for translucent to semi-translucent material with dark, branching, organic-looking patterns. The base color is typically white, gray, or brownish. It can be found in various locations worldwide, including Brazil, India, the USA (Oregon, Montana), and Mexico. In the field, look for nodules or veins in volcanic or sedimentary rocks, often found alongside other forms of chalcedony. It's identified by its hardness, lack of distinct cleavage, and characteristic dendritic patterns.