Billitonite is a rare regional variety of Tektite from Belitung Island, Indonesia, formerly known as Billiton Island. It is part of the wider Australasian strewn field, which formed around 790,000 years ago during a major impact event that dispersed natural glass across a vast area of Southeast Asia, Australia, and the Indian Ocean region. Locally, Billitonite is often known as ‘Batu Satam’, and it has a strong cultural and collector identity on Belitung Island.

Billitonites are typically glossy black and are especially recognised for their deep natural grooves, pits, and sculpted surface textures. Many specimens are rounded or irregular in form, with a bright enamel-like lustre that sets them apart from more common Indochinites. Much of the material has historically been recovered from alluvial tin-mining areas, where pieces were found below the surface in association with local sediments.

Studying Billitonite provides insight into the regional diversity of the Australasian Tektite strewn field and the effects of long-term terrestrial preservation on natural impact glass. For collectors, Billitonites are desirable because of their limited locality, distinctive black glassy appearance, and strong association with Belitung Island. Each specimen represents a natural glass formed by cosmic impact processes and preserved as one of Indonesia’s most recognisable Tektite materials.