Kauri gum is a fossilised resin extracted from Ancient Kauri, which is made into crafts such as jewellery. Kauri gum formed when resin from kauri trees leaked out through fractures or cracks in the bark, hardening with the exposure to air. Lumps commonly fell to the ground and became covered with soil and forest litter, eventually fossilising. Other lumps formed as branches forked or trees were damaged, which released the resin. Like amber, kauri gum sometimes includes insects and plant material.
Kauri gum is a type of copal. Kauri gum was found to be particularly good for this, and from the mid-1840s was exported to London and America. Tentative exports had begun a few years earlier.
The gum varied in color depending on the condition of the original tree. It also depended on where the gum had formed and how long it had been buried. Colors ranged from chalky-white, through red-brown to black; the most prized was a pale gold, as it was hard and translucent. The majority were the size of acorns, although some were found which weighed a few pounds. Kauri gum shares a few characteristics with amber, another fossilised resin found in the Northern Hemisphere, but where amber can be dated as millions of years old, carbon-dating suggests the age of most kauri gum is up to 50,000 years which is the limit of C14 radio carbon dating.