Billitonite tektites are from Belitung, Indonesia. They are part of the Australasian meteor impact 800,000 years ago. They were discovered when mining for tin and were collected by the local tin miners.
 
These rare tektites are black in appearance and some of them have deep etching and a high gloss from the acidic soil and water on Belitung. However, some have lighter etching and less surface gloss.