Tree agate is a form of chalcedony, which is microcrystalline quartz. SiO2. It's proper name is dendritic quartz, or dendritic agate. The main body is a dirty white with a hint of green. The tree part of the description is an obvious reference to the similarity of the branches of a tree. The green inclusions are dendritic manganese with maybe a small amount of iron. The specimen is from S.W. Australia,and was collected by the club's co-founder, Jim Nicholls, while working in Australia.