Here is a piece of Snowflake obsidian from Lipari in my collection. Also known as Cristobalite, it is glass formed by the volcano. Many pieces of volcanic glass are a solid black and sometimes quite clear as well as a number of earth tones. These rocks found around volcanoes are often made into jewelry and they can be purchased on the islands.
A ring purchased in Malfa by my cousin.
Obsidian was an early source of wealth for the islands before the advent of metal tools as they are easily worked into very sharp edges in any shape desired. Flint is another mineral that can be worked in a similar way. This obsidian was traded all over the Mediterranean in the stone age and in the early metal ages as the use of copper and bronze was in the early stages of development and where those metals were expensive or unobtainable, they continued in use for centuries. There was a huge trading network in place by the 2nd millennium BC.
Notice on this piece of obsidian that there are a number of breaks that form a very
specific pattern. this is conchoidal fracture. In this case, the top left at about
the 11 o'clock position was struck or hit and the fracture radiated out
toward the bottom right. Conchoidal means shell like, and this is easy to see.