Quantity: 1 kilogram Average size range: 25 to 40 millimeters Much like moss agate, tree agate is a composite form of chalcedony, formed from primarily white or milky quartz with green inclusions of iron oxide and manganese oxide. Tree agate tends to be more translucent than moss agate, and the dendritic inclusions tend to be straighter like tree branches rather than wispy or threaded.