What has happened so far......
Thousands of years,people didn't know how to make glass,and so they used natural glass.Natural glass is made in two ways.Firstly,glass can be made during a storm. When lightning his sand,thin glass tubes are produced in the heat. These kinds of glass are called fulgurites. Secondly,glass can be made when a volcano erupts.The rock that comes out of the volcano is very not so it is liquid.It cools very quickly and becomes glass. These kinds of glass are called obsidian. You can fine this kind of natural glass in the islands between Greece and Turkey where they are lots of volcanoes.