Moss agate

Refers to a variety of agate containing brown or black moss- or tree-like dendritic forms. It is typically a grayish to milky-white agate, which is a variety of the silica mineral quartz. It contains opaque, dark-colored inclusions with feathery, branching forms that resemble ferns, moss, or other vegetation but that are in fact of inorganic origin, mainly manganese and iron oxides. Most examples of moss agate are found as fragments of weathered from volcanic rocks from India, Brazil, Uruguay, central Europe, and the western United States. The stone has historically been used for ornamental purposes, often cut in flat or rounded forms, and sometimes dyed to improve its color.